Effect of stretch on calcium channel currents recorded from the antral circular myocytes of guinea-pig stomach

Abstract

The effect of membrane stretch on voltage-activated Ba2+ current (IBa) was studied in antral circular myocytes of guinea-pig using the whole- cell patch-clamp technique. The changes in cell volume were elicited by superfusing the myocytes with anisosmotic solutions. Hyposmotic superfusate (202 mosmol/l) induced cell swelling and increased peak values of IBa at 0 mV (from -406.6 +/- 45.5 pA to -547.5 +/- 65.6 pA, mean +/- SEM, n = 8) and hyperosmotic superfusate (350 mosmol/l) induced cell shrinkage and decreased peak values of IBa at 0 mV (to -269.5 +/- 39.1 pA, n = 8). Such changes were reversible and the extent of change was dependent on the osmolarity of superfusate. The values of normalized IBa at 0 mV were 1.43 +/- 0.04, 1.30 +/- 0.06, 1.23 +/- 0.04, 1.19 +/- 0.04, 1 and 0. 68 +/- 0.06 at 202, 220, 245, 267, 290 and 350 mosmol/l, respectively (n = 8). IBa was almost completely blocked by nicardipine (5 microM) under hyposmotic conditions. The values of steady-state half-inactivation voltage (-37.7 +/- 3.3 and -36.5 +/- 2.6 mV, under control and hyposmotic conditions, respectively) or the half-activation voltage (-13.6 +/- 2.3 and -13.9 +/- 1.9 mV) of IBa were not significantly changed (P > 0.05, n = 6). Cell membrane capacitance was slightly increased from 50.00 +/- 2.86 pF to 50.22 +/- 2.82 pF by a hyposmotic superfusate (P < 0.05, n = 6). It is suggested that cell swelling increases voltage-operated L-type calcium channel current and that such a property is related to the response of gastric smooth muscle to mechanical stimuli.

The Involvement of Calcium Mobilization in the Calcium-Activated Potassium Currents Activated by Hyposmotic Swelling in Gastric Antral Circular Myocytes of the Guinea-Pig.

“…The latter current is very similar in duration. It is a hyposmotic swelling-induced increase of L-type calcium currents [14]. Thus I K(Ca) may play an important role in regulating cell tone in antral circular myocytes during hyposmotic conditions.…”

“…Other experiments have shown that I K(Ca) is activated by an intracellular Ca 2ϩ signal that is released from intracellular calcium stores during RVD [13]. But the effect of hyposmotic swelling on I K(Ca) and the role of intracellular or extracellular Ca 2ϩ in gastric smooth muscle cells has not been investigated.In our previous study, we reported that the voltageoperated calcium current (I Ca ) was increased [14] and that the volume-sensitive chloride current (I Cl ) was activated by hyposmotic swelling [15] in gastric antral myocytes of the guinea-pig. In the present study, we Key words: gastric smooth muscle cell, Ca 2ϩ -activated K ϩ current, Ca 2ϩ -induced Ca 2ϩ release, swelling.…”

“…In our previous study, we reported that the voltageoperated calcium current (I Ca ) was increased [14] and that the volume-sensitive chloride current (I Cl ) was activated by hyposmotic swelling [15] in gastric antral myocytes of the guinea-pig. In the present study, we Key words: gastric smooth muscle cell, Ca 2ϩ -activated K ϩ current, Ca 2ϩ -induced Ca 2ϩ release, swelling.…”

Cytochalasin D reduces Ca2+ currents via cofilin‐activated depolymerization of F‐actin in guinea‐pig cardiomyocytes

“…In vascular and cardiac myocytes, cell shrinkage or swelling in hyper-or hyposmotic media has been reported to increase or decrease I Ca , respectively (Langton, 1993;Matsuda et al 1996;Xu et al 1996). Possibly, augmentation of I Ca by cell swelling is mediated by an increased mechanical strain from the cytoskeleton to the Ca 2+ channel protein.…”

Role of arachidonic acid in hyposmotic membrane stretch-induced increase in calcium-activated potassium currents in gastric myocytes1

“…In our previous study, AA and other unsaturated fatty acids directly inhibited calcium currents [12] and muscarinic currents [13] . For both AA and hyposmotic membrane stretch-activated I K(Ca) [14,15] , activation by hyposmotic membrane stretch is associated with calcium-induced calcium release (CICR) [16] , which is triggered by extracellular calcium influx through the stretch-activated channels (SAC) in gastric antral circular myocytes of the guinea pig.…”