Limits...
Swelling-activated Gd3+-sensitive cation current and cell volume regulation in rabbit ventricular myocytes.

Clemo HF, Baumgarten CM - J. Gen. Physiol. (1997)

Bottom Line: Increasing bath K+ increased gCir,swell but decreased rectification.Besides its effects on cell volume, ICir,swell is expected to cause diastolic depolarization.Activation of ICir, swell also is likely to affect contraction and other physiological processes in myocytes.

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine (Cardiology), Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298, USA.

ABSTRACT
The role of swelling-activated currents in cell volume regulation is unclear. Currents elicited by swelling rabbit ventricular myocytes in solutions with 0.6-0.9x normal osmolarity were studied using amphotericin perforated patch clamp techniques, and cell volume was examined concurrently by digital video microscopy. Graded swelling caused graded activation of an inwardly rectifying, time-independent cation current (ICir,swell) that was reversibly blocked by Gd3+, but ICir,swell was not detected in isotonic or hypertonic media. This current was not related to IK1 because it was insensitive to Ba2+. The PK/PNa ratio for ICir,swell was 5.9 +/- 0.3, implying that inward current is largely Na+ under physiological conditions. Increasing bath K+ increased gCir,swell but decreased rectification. Gd3+ block was fitted with a K0.5 of 1.7 +/- 0.3 microM and Hill coefficient, n, of 1.7 +/- 0.4. Exposure to Gd3+ also reduced hypotonic swelling by up to approximately 30%, and block of current preceded the volume change by approximately 1 min. Gd3+-induced cell shrinkage was proportional to ICir,swell when ICir,swell was varied by graded swelling or Gd3+ concentration and was voltage dependent, reflecting the voltage dependence of ICir,swell. Integrating the blocked ion flux and calculating the resulting change in osmolarity suggested that ICir,swell was sufficient to explain the majority of the volume change at -80 mV. In addition, swelling activated an outwardly rectifying Cl- current, ICl,swell. This current was absent after Cl- replacement, reversed at ECl, and was blocked by 1 mM 9-anthracene carboxylic acid. Block of ICl,swell provoked a 28% increase in swelling in hypotonic media. Thus, both cation and anion swelling-activated currents modulated the volume of ventricular myocytes. Besides its effects on cell volume, ICir,swell is expected to cause diastolic depolarization. Activation of ICir, swell also is likely to affect contraction and other physiological processes in myocytes.

Show MeSH

Related in: MedlinePlus

Response to Gd3+ depends on bath osmolarity. I-V relationships and cell volumes were determined in the absence and  presence of 10 μM Gd3+ in 0.6T–1.5T bath solutions, n = 5 cells.  (A) Average Gd3+-sensitive currents. (B) Cell volumes in the absence and presence of Gd3+; cell volumes in hypotonic solution  were reduced by Gd3+. Both the Gd3+-sensitive current and the  Gd3+-induced reduction of volume progressively increased as bath  osmolarity was decreased; maximum responses were observed in  ≤0.7T. In contrast, Gd3+ did not alter the I-V relationship or cell  volume in isotonic (1T) or hypertonic (1.5T) solutions. (C) Gd3+-sensitive current and cell shrinkage are plotted as a function of  bath-relative osmolarity. Eh, −80 mV; bath, 0 Cl−; pipette, low Cl−.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC2229368&req=5

Figure 10: Response to Gd3+ depends on bath osmolarity. I-V relationships and cell volumes were determined in the absence and presence of 10 μM Gd3+ in 0.6T–1.5T bath solutions, n = 5 cells. (A) Average Gd3+-sensitive currents. (B) Cell volumes in the absence and presence of Gd3+; cell volumes in hypotonic solution were reduced by Gd3+. Both the Gd3+-sensitive current and the Gd3+-induced reduction of volume progressively increased as bath osmolarity was decreased; maximum responses were observed in ≤0.7T. In contrast, Gd3+ did not alter the I-V relationship or cell volume in isotonic (1T) or hypertonic (1.5T) solutions. (C) Gd3+-sensitive current and cell shrinkage are plotted as a function of bath-relative osmolarity. Eh, −80 mV; bath, 0 Cl−; pipette, low Cl−.

Mentions: Gd3+-sensitive cation SAC activity in cell-attached patches is a graded function of the negative pressure applied to the pipette and the degree of membrane stretch (Guharay and Sachs, 1984; Sigurdson et al., 1987). For a range of stimuli, the open probability of the nonselective cation mechanoelectrical transduction channel in the bullfrog saccular hair cell has been postulated to be linearly related to membrane tension (Howard et al., 1988), whereas Guharay and Sachs (1984) postulated that gating of the cation SAC in tissue-cultured embryonic chick skeletal muscle cells varies with the square of membrane tension. One might expect the magnitude of ICir,swell and Gd3+-induced volume changes also would depend on the amount of swelling-induced membrane stretch. To test this idea, myocytes were placed in a series of hypotonic (0.6–0.9T), isotonic (1T), and hypertonic (1.5T) solutions, and the I-V relationship and relative cell volume were monitored. ICir,swell was measured as the difference between the I-V relationships ± 10 μM Gd3+ in each of the superfusates. Fig. 10 A shows that Gd3+ did not affect membrane current in isotonic solution or when myocytes were shrunken in 1.5T solution. On the other hand, as bath solution osmolarity was gradually stepped from 1 to 0.6T, ICir,swell increased in a graded fashion. At the same time, osmotic swelling in the presence of Gd3+ was attenuated (Fig. 10 B). These effects are summarized in Fig. 10 C where Gd3+-sensitive current and cell shrinkage are plotted versus bath osmolarity.


Swelling-activated Gd3+-sensitive cation current and cell volume regulation in rabbit ventricular myocytes.

Clemo HF, Baumgarten CM - J. Gen. Physiol. (1997)

Response to Gd3+ depends on bath osmolarity. I-V relationships and cell volumes were determined in the absence and  presence of 10 μM Gd3+ in 0.6T–1.5T bath solutions, n = 5 cells.  (A) Average Gd3+-sensitive currents. (B) Cell volumes in the absence and presence of Gd3+; cell volumes in hypotonic solution  were reduced by Gd3+. Both the Gd3+-sensitive current and the  Gd3+-induced reduction of volume progressively increased as bath  osmolarity was decreased; maximum responses were observed in  ≤0.7T. In contrast, Gd3+ did not alter the I-V relationship or cell  volume in isotonic (1T) or hypertonic (1.5T) solutions. (C) Gd3+-sensitive current and cell shrinkage are plotted as a function of  bath-relative osmolarity. Eh, −80 mV; bath, 0 Cl−; pipette, low Cl−.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2229368&req=5

Figure 10: Response to Gd3+ depends on bath osmolarity. I-V relationships and cell volumes were determined in the absence and presence of 10 μM Gd3+ in 0.6T–1.5T bath solutions, n = 5 cells. (A) Average Gd3+-sensitive currents. (B) Cell volumes in the absence and presence of Gd3+; cell volumes in hypotonic solution were reduced by Gd3+. Both the Gd3+-sensitive current and the Gd3+-induced reduction of volume progressively increased as bath osmolarity was decreased; maximum responses were observed in ≤0.7T. In contrast, Gd3+ did not alter the I-V relationship or cell volume in isotonic (1T) or hypertonic (1.5T) solutions. (C) Gd3+-sensitive current and cell shrinkage are plotted as a function of bath-relative osmolarity. Eh, −80 mV; bath, 0 Cl−; pipette, low Cl−.
Mentions: Gd3+-sensitive cation SAC activity in cell-attached patches is a graded function of the negative pressure applied to the pipette and the degree of membrane stretch (Guharay and Sachs, 1984; Sigurdson et al., 1987). For a range of stimuli, the open probability of the nonselective cation mechanoelectrical transduction channel in the bullfrog saccular hair cell has been postulated to be linearly related to membrane tension (Howard et al., 1988), whereas Guharay and Sachs (1984) postulated that gating of the cation SAC in tissue-cultured embryonic chick skeletal muscle cells varies with the square of membrane tension. One might expect the magnitude of ICir,swell and Gd3+-induced volume changes also would depend on the amount of swelling-induced membrane stretch. To test this idea, myocytes were placed in a series of hypotonic (0.6–0.9T), isotonic (1T), and hypertonic (1.5T) solutions, and the I-V relationship and relative cell volume were monitored. ICir,swell was measured as the difference between the I-V relationships ± 10 μM Gd3+ in each of the superfusates. Fig. 10 A shows that Gd3+ did not affect membrane current in isotonic solution or when myocytes were shrunken in 1.5T solution. On the other hand, as bath solution osmolarity was gradually stepped from 1 to 0.6T, ICir,swell increased in a graded fashion. At the same time, osmotic swelling in the presence of Gd3+ was attenuated (Fig. 10 B). These effects are summarized in Fig. 10 C where Gd3+-sensitive current and cell shrinkage are plotted versus bath osmolarity.

Bottom Line: Increasing bath K+ increased gCir,swell but decreased rectification.Besides its effects on cell volume, ICir,swell is expected to cause diastolic depolarization.Activation of ICir, swell also is likely to affect contraction and other physiological processes in myocytes.

View Article: PubMed Central - PubMed

Affiliation: Department of Internal Medicine (Cardiology), Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298, USA.

ABSTRACT
The role of swelling-activated currents in cell volume regulation is unclear. Currents elicited by swelling rabbit ventricular myocytes in solutions with 0.6-0.9x normal osmolarity were studied using amphotericin perforated patch clamp techniques, and cell volume was examined concurrently by digital video microscopy. Graded swelling caused graded activation of an inwardly rectifying, time-independent cation current (ICir,swell) that was reversibly blocked by Gd3+, but ICir,swell was not detected in isotonic or hypertonic media. This current was not related to IK1 because it was insensitive to Ba2+. The PK/PNa ratio for ICir,swell was 5.9 +/- 0.3, implying that inward current is largely Na+ under physiological conditions. Increasing bath K+ increased gCir,swell but decreased rectification. Gd3+ block was fitted with a K0.5 of 1.7 +/- 0.3 microM and Hill coefficient, n, of 1.7 +/- 0.4. Exposure to Gd3+ also reduced hypotonic swelling by up to approximately 30%, and block of current preceded the volume change by approximately 1 min. Gd3+-induced cell shrinkage was proportional to ICir,swell when ICir,swell was varied by graded swelling or Gd3+ concentration and was voltage dependent, reflecting the voltage dependence of ICir,swell. Integrating the blocked ion flux and calculating the resulting change in osmolarity suggested that ICir,swell was sufficient to explain the majority of the volume change at -80 mV. In addition, swelling activated an outwardly rectifying Cl- current, ICl,swell. This current was absent after Cl- replacement, reversed at ECl, and was blocked by 1 mM 9-anthracene carboxylic acid. Block of ICl,swell provoked a 28% increase in swelling in hypotonic media. Thus, both cation and anion swelling-activated currents modulated the volume of ventricular myocytes. Besides its effects on cell volume, ICir,swell is expected to cause diastolic depolarization. Activation of ICir, swell also is likely to affect contraction and other physiological processes in myocytes.

Show MeSH
Related in: MedlinePlus