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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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Kslow current is K+ selective. (A, bottom) After the train of depolarizations, the membrane potential was held for 10 s at voltages between −40 and −80 mV as indicated schematically by the pulse protocol. (A, top) Membrane currents recorded at −50 mV after the train when the extracellular medium contained 3.6 or 15 mM K+ as indicated. Note that the currents go in opposite directions. (B) The peak tail currents recorded at membrane potentials between −80 and −40 mV before and after elevation of extracellular K+ from 3.6 mM (▪) to 15 mM (▴). The amplitude of the current was measured as illustrated in B. The arrows indicate the reversal potentials recorded at low and high extracellular K+.
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Figure 2: Kslow current is K+ selective. (A, bottom) After the train of depolarizations, the membrane potential was held for 10 s at voltages between −40 and −80 mV as indicated schematically by the pulse protocol. (A, top) Membrane currents recorded at −50 mV after the train when the extracellular medium contained 3.6 or 15 mM K+ as indicated. Note that the currents go in opposite directions. (B) The peak tail currents recorded at membrane potentials between −80 and −40 mV before and after elevation of extracellular K+ from 3.6 mM (▪) to 15 mM (▴). The amplitude of the current was measured as illustrated in B. The arrows indicate the reversal potentials recorded at low and high extracellular K+.

Mentions: In the intact islet, the β cells are electrically coupled and electrical activity in neighboring cells spreads into the voltage-clamped cell via the gap junctions (Mears et al. 1995; Fig. 1 D and 3). To allow voltage-clamp measurements without interference by currents originating from the neighboring cells, the glucose concentration was usually lowered to 5 mM to suppress glucose-induced electrical activity. Electrical activity was then simulated by application of a sequence of voltage-clamp pulses. This consisted of depolarization from −70 to −40 mV for 5 s, followed by a series of 26 simulated “action potentials.” The latter consisted of a voltage ramp between −40 and 0 mV (100 ms) followed by a ramp from 0 to −40 mV (100 ms). The action potential waveform was applied at a frequency of 5 Hz. This voltage range, frequency, and duration approximate the β cell action potential. Subsequent to the train of voltage-clamp pulses, the cell was held at −40 mV for 10 or 20 s (except in Fig. 2 A and 3 D) to facilitate the observation of K+ currents. The interval between two successive stimulation series was normally 0.5–2 min to allow complete recovery from inactivation. All experiments were carried out using the perforated patch whole-cell configuration (Lindau and Fernandez 1986; Horn and Marty 1988) and were conducted at 30–32°C. During the experiments, the islet was continuously superfused with extracellular medium at a rate of 1–2 ml/min.


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)

Kslow current is K+ selective. (A, bottom) After the train of depolarizations, the membrane potential was held for 10 s at voltages between −40 and −80 mV as indicated schematically by the pulse protocol. (A, top) Membrane currents recorded at −50 mV after the train when the extracellular medium contained 3.6 or 15 mM K+ as indicated. Note that the currents go in opposite directions. (B) The peak tail currents recorded at membrane potentials between −80 and −40 mV before and after elevation of extracellular K+ from 3.6 mM (▪) to 15 mM (▴). The amplitude of the current was measured as illustrated in B. The arrows indicate the reversal potentials recorded at low and high extracellular K+.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2230648&req=5

Figure 2: Kslow current is K+ selective. (A, bottom) After the train of depolarizations, the membrane potential was held for 10 s at voltages between −40 and −80 mV as indicated schematically by the pulse protocol. (A, top) Membrane currents recorded at −50 mV after the train when the extracellular medium contained 3.6 or 15 mM K+ as indicated. Note that the currents go in opposite directions. (B) The peak tail currents recorded at membrane potentials between −80 and −40 mV before and after elevation of extracellular K+ from 3.6 mM (▪) to 15 mM (▴). The amplitude of the current was measured as illustrated in B. The arrows indicate the reversal potentials recorded at low and high extracellular K+.
Mentions: In the intact islet, the β cells are electrically coupled and electrical activity in neighboring cells spreads into the voltage-clamped cell via the gap junctions (Mears et al. 1995; Fig. 1 D and 3). To allow voltage-clamp measurements without interference by currents originating from the neighboring cells, the glucose concentration was usually lowered to 5 mM to suppress glucose-induced electrical activity. Electrical activity was then simulated by application of a sequence of voltage-clamp pulses. This consisted of depolarization from −70 to −40 mV for 5 s, followed by a series of 26 simulated “action potentials.” The latter consisted of a voltage ramp between −40 and 0 mV (100 ms) followed by a ramp from 0 to −40 mV (100 ms). The action potential waveform was applied at a frequency of 5 Hz. This voltage range, frequency, and duration approximate the β cell action potential. Subsequent to the train of voltage-clamp pulses, the cell was held at −40 mV for 10 or 20 s (except in Fig. 2 A and 3 D) to facilitate the observation of K+ currents. The interval between two successive stimulation series was normally 0.5–2 min to allow complete recovery from inactivation. All experiments were carried out using the perforated patch whole-cell configuration (Lindau and Fernandez 1986; Horn and Marty 1988) and were conducted at 30–32°C. During the experiments, the islet was continuously superfused with extracellular medium at a rate of 1–2 ml/min.

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