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Activation of Ca(2+)-dependent K(+) channels contributes to rhythmic firing of action potentials in mouse pancreatic beta cells.

Göpel SO, Kanno T, Barg S, Eliasson L, Galvanovskis J, Renström E, Rorsman P - J. Gen. Physiol. (1999)

Bottom Line: The current was dependent on Ca(2+) influx but unaffected by apamin and charybdotoxin, two blockers of Ca(2+)-activated K(+) channels, and was insensitive to tolbutamide (a blocker of ATP-regulated K(+) channels) but partially (>60%) blocked by high (10-20 mM) concentrations of tetraethylammonium.This is similar to the interval between two successive bursts of action potentials.We propose that this Ca(2+)-activated K(+) current plays an important role in the generation of oscillatory electrical activity in the beta cell.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiological Sciences, Division of Molecular and Cellular Physiology, Lund University, SE-223 62 Lund, Sweden.

ABSTRACT
We have applied the perforated patch whole-cell technique to beta cells within intact pancreatic islets to identify the current underlying the glucose-induced rhythmic firing of action potentials. Trains of depolarizations (to simulate glucose-induced electrical activity) resulted in the gradual (time constant: 2.3 s) development of a small (<0.8 nS) K(+) conductance. The current was dependent on Ca(2+) influx but unaffected by apamin and charybdotoxin, two blockers of Ca(2+)-activated K(+) channels, and was insensitive to tolbutamide (a blocker of ATP-regulated K(+) channels) but partially (>60%) blocked by high (10-20 mM) concentrations of tetraethylammonium. Upon cessation of electrical stimulation, the current deactivated exponentially with a time constant of 6.5 s. This is similar to the interval between two successive bursts of action potentials. We propose that this Ca(2+)-activated K(+) current plays an important role in the generation of oscillatory electrical activity in the beta cell.

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Train of action potentials elicits an outward current in β cells. (A) Membrane potential oscillations in a β cell exposed to 10 mM glucose. The glucose concentration was lowered to 5 mM as indicated above the voltage trace. *The amplifier was switched from the current-clamp into the voltage-clamp mode, the membrane potential held at −70 mV, and the command voltage varied as indicated. (B) The membrane currents elicited by the pulse train (C, top). Note time-dependent decline of outward current. (C, bottom) Change of holding current displayed on an expanded vertical scale. Note gradual development of a holding current. Same experiment as in B. (D) Membrane potential recording from the same cell as in C before lowering the glucose concentration. In C and D, the vertical line marks the temporal relationship between cessation of stimulation and the onset of rapid repolarization (left) and the onset of rapid depolarization during the subsequent burst (right). The horizontal lines indicate (from top to bottom) the steady state holding current at −40 mV, the plateau potential from which the cell repolarizes upon termination of the burst, and the most negative membrane potential attained between two bursts. (E) Membrane potential recording from an isolated (dispersed) β cell maintained in tissue culture. The glucose concentration was changed from 10 to 0 mM as indicated above the voltage trace. (F) Currents elicited by the train of depolarizations (bottom) in the presence of 10 (top) and 5 (middle) mM glucose. The inward current (indicated by the horizontal line above the current trace) is due to a burst of action potentials generated in a neighboring β cell. Note that step current elicited when stepping from −70 to −40 mV is larger at 5 than at 10 mM glucose, reflecting greater activity of the KATP channels.
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Figure 1: Train of action potentials elicits an outward current in β cells. (A) Membrane potential oscillations in a β cell exposed to 10 mM glucose. The glucose concentration was lowered to 5 mM as indicated above the voltage trace. *The amplifier was switched from the current-clamp into the voltage-clamp mode, the membrane potential held at −70 mV, and the command voltage varied as indicated. (B) The membrane currents elicited by the pulse train (C, top). Note time-dependent decline of outward current. (C, bottom) Change of holding current displayed on an expanded vertical scale. Note gradual development of a holding current. Same experiment as in B. (D) Membrane potential recording from the same cell as in C before lowering the glucose concentration. In C and D, the vertical line marks the temporal relationship between cessation of stimulation and the onset of rapid repolarization (left) and the onset of rapid depolarization during the subsequent burst (right). The horizontal lines indicate (from top to bottom) the steady state holding current at −40 mV, the plateau potential from which the cell repolarizes upon termination of the burst, and the most negative membrane potential attained between two bursts. (E) Membrane potential recording from an isolated (dispersed) β cell maintained in tissue culture. The glucose concentration was changed from 10 to 0 mM as indicated above the voltage trace. (F) Currents elicited by the train of depolarizations (bottom) in the presence of 10 (top) and 5 (middle) mM glucose. The inward current (indicated by the horizontal line above the current trace) is due to a burst of action potentials generated in a neighboring β cell. Note that step current elicited when stepping from −70 to −40 mV is larger at 5 than at 10 mM glucose, reflecting greater activity of the KATP channels.

Mentions: Unless otherwise indicated, the electrophysiological experiments were carried out on β cells in intact islets. NMRI mice were purchased from a commercial breeder (Moellegaard). The mice were stunned by a blow against the head and killed by cervical dislocation and the pancreas quickly removed. Collagenase (2 mg) was dissolved in Hank's buffer and injected into the pancreatic duct. Pancreatic islets were isolated by gentle collagenase digestion (25 min, 37°C). Islets thus isolated were subsequently maintained in short-term tissue culture (<16 h) in RPMI 1640 containing 5 mM glucose and 10% (vol/vol) fetal calf serum (Flow Laboratories) and supplemented with 100 μg/ml streptomycin and 100 IU/ml penicillin (both from Northumbria Biologicals, Ltd.). The experiments in Fig. 1C and some of those displayed in Fig. 5 were carried out on dispersed β cells. These were prepared by shaking islets in Ca2+-free solution. The resultant cell suspension was plated on glass cover slips (diameter: 22 mm) or Nunc plastic petri dishes and maintained in tissue culture for up to 48 h using the tissue culture medium mentioned above.


Activation of Ca(2+)-dependent K(+) channels contributes to rhythmic firing of action potentials in mouse pancreatic beta cells.

Göpel SO, Kanno T, Barg S, Eliasson L, Galvanovskis J, Renström E, Rorsman P - J. Gen. Physiol. (1999)

Train of action potentials elicits an outward current in β cells. (A) Membrane potential oscillations in a β cell exposed to 10 mM glucose. The glucose concentration was lowered to 5 mM as indicated above the voltage trace. *The amplifier was switched from the current-clamp into the voltage-clamp mode, the membrane potential held at −70 mV, and the command voltage varied as indicated. (B) The membrane currents elicited by the pulse train (C, top). Note time-dependent decline of outward current. (C, bottom) Change of holding current displayed on an expanded vertical scale. Note gradual development of a holding current. Same experiment as in B. (D) Membrane potential recording from the same cell as in C before lowering the glucose concentration. In C and D, the vertical line marks the temporal relationship between cessation of stimulation and the onset of rapid repolarization (left) and the onset of rapid depolarization during the subsequent burst (right). The horizontal lines indicate (from top to bottom) the steady state holding current at −40 mV, the plateau potential from which the cell repolarizes upon termination of the burst, and the most negative membrane potential attained between two bursts. (E) Membrane potential recording from an isolated (dispersed) β cell maintained in tissue culture. The glucose concentration was changed from 10 to 0 mM as indicated above the voltage trace. (F) Currents elicited by the train of depolarizations (bottom) in the presence of 10 (top) and 5 (middle) mM glucose. The inward current (indicated by the horizontal line above the current trace) is due to a burst of action potentials generated in a neighboring β cell. Note that step current elicited when stepping from −70 to −40 mV is larger at 5 than at 10 mM glucose, reflecting greater activity of the KATP channels.
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Related In: Results  -  Collection

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Figure 1: Train of action potentials elicits an outward current in β cells. (A) Membrane potential oscillations in a β cell exposed to 10 mM glucose. The glucose concentration was lowered to 5 mM as indicated above the voltage trace. *The amplifier was switched from the current-clamp into the voltage-clamp mode, the membrane potential held at −70 mV, and the command voltage varied as indicated. (B) The membrane currents elicited by the pulse train (C, top). Note time-dependent decline of outward current. (C, bottom) Change of holding current displayed on an expanded vertical scale. Note gradual development of a holding current. Same experiment as in B. (D) Membrane potential recording from the same cell as in C before lowering the glucose concentration. In C and D, the vertical line marks the temporal relationship between cessation of stimulation and the onset of rapid repolarization (left) and the onset of rapid depolarization during the subsequent burst (right). The horizontal lines indicate (from top to bottom) the steady state holding current at −40 mV, the plateau potential from which the cell repolarizes upon termination of the burst, and the most negative membrane potential attained between two bursts. (E) Membrane potential recording from an isolated (dispersed) β cell maintained in tissue culture. The glucose concentration was changed from 10 to 0 mM as indicated above the voltage trace. (F) Currents elicited by the train of depolarizations (bottom) in the presence of 10 (top) and 5 (middle) mM glucose. The inward current (indicated by the horizontal line above the current trace) is due to a burst of action potentials generated in a neighboring β cell. Note that step current elicited when stepping from −70 to −40 mV is larger at 5 than at 10 mM glucose, reflecting greater activity of the KATP channels.
Mentions: Unless otherwise indicated, the electrophysiological experiments were carried out on β cells in intact islets. NMRI mice were purchased from a commercial breeder (Moellegaard). The mice were stunned by a blow against the head and killed by cervical dislocation and the pancreas quickly removed. Collagenase (2 mg) was dissolved in Hank's buffer and injected into the pancreatic duct. Pancreatic islets were isolated by gentle collagenase digestion (25 min, 37°C). Islets thus isolated were subsequently maintained in short-term tissue culture (<16 h) in RPMI 1640 containing 5 mM glucose and 10% (vol/vol) fetal calf serum (Flow Laboratories) and supplemented with 100 μg/ml streptomycin and 100 IU/ml penicillin (both from Northumbria Biologicals, Ltd.). The experiments in Fig. 1C and some of those displayed in Fig. 5 were carried out on dispersed β cells. These were prepared by shaking islets in Ca2+-free solution. The resultant cell suspension was plated on glass cover slips (diameter: 22 mm) or Nunc plastic petri dishes and maintained in tissue culture for up to 48 h using the tissue culture medium mentioned above.

Bottom Line: The current was dependent on Ca(2+) influx but unaffected by apamin and charybdotoxin, two blockers of Ca(2+)-activated K(+) channels, and was insensitive to tolbutamide (a blocker of ATP-regulated K(+) channels) but partially (>60%) blocked by high (10-20 mM) concentrations of tetraethylammonium.This is similar to the interval between two successive bursts of action potentials.We propose that this Ca(2+)-activated K(+) current plays an important role in the generation of oscillatory electrical activity in the beta cell.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiological Sciences, Division of Molecular and Cellular Physiology, Lund University, SE-223 62 Lund, Sweden.

ABSTRACT
We have applied the perforated patch whole-cell technique to beta cells within intact pancreatic islets to identify the current underlying the glucose-induced rhythmic firing of action potentials. Trains of depolarizations (to simulate glucose-induced electrical activity) resulted in the gradual (time constant: 2.3 s) development of a small (<0.8 nS) K(+) conductance. The current was dependent on Ca(2+) influx but unaffected by apamin and charybdotoxin, two blockers of Ca(2+)-activated K(+) channels, and was insensitive to tolbutamide (a blocker of ATP-regulated K(+) channels) but partially (>60%) blocked by high (10-20 mM) concentrations of tetraethylammonium. Upon cessation of electrical stimulation, the current deactivated exponentially with a time constant of 6.5 s. This is similar to the interval between two successive bursts of action potentials. We propose that this Ca(2+)-activated K(+) current plays an important role in the generation of oscillatory electrical activity in the beta cell.

Show MeSH
Related in: MedlinePlus