VOLUME-SENSITIVE CHLORIDE CURRENT ACTIVATED BY HYPOSMOTIC SWELLING INANTRAL GASTRIC MYOCYTES OF THE GUINEA-PIG

The characteristics of volume-sensitive chloride current (I-Cl) induce d by osmotic cell swelling were studied using the whole-cell patch-cla mp technique and cell diameters of antral circular guinea-pig myocytes were simultaneously measured under isosmotic and hyposmotic condition s by using a video image analysis system. At -60 mV, osmotic cell swel ling (200 mosmol/l) activated a sustained inward current. Instantaneou s current/voltage (I-V) relations obtained by step voltage pulses show ed an outward rectification. At potentials above +40 mV, the current e xhibited time-dependent decay. The outward current amplitude was decre ased and the reversal potential was shifted to more positive potential s by replacement of external Cl- with gluconate(-), while the current amplitude and the I/V relation were not affected by replacing extracel lular Na+ with N-methyl-D-glucamine. The anion permeability sequence o f the swelling-induced current was I- (1.80) > Br- (1.31) > Cl- (1) > F- (0.85) > gluconate(-) (0.18). The I-Cl was effectively inhibited by the Cl- channel blockers, 4,4'-diisothiocyanatostilbene-2,2'-disulpho nic acid (DIDS, 100 mu M), and niflumic acid (10 mu M). DIDS suppresse d outward current more effectively than inward current. Also, the I-Cl was dose-dependently inhibited by arachidonic acid, an unsaturated fa tty acid and also inhibited by other unsaturated fatty acids (linoleic acid and oleic acid) but not by stearic acid, a saturated fatty acid. The inhibitory effect of arachidonic acid on I-Cl was not prevented b y indomethacin, a cyclo-oxygenase inhibitor and chelerythrine, a prote in kinase C inhibitor. Under whole-cell patch-clamp conditions, the ce ll diameter was continuously measured using video image analysis, whic h reflects the change in cell volume. A hyposmotic-stimulation-induced increase of cell diameter was followed by I-Cl activation. In intact single gastric myocytes, relatively severe hyposmotic (176 mosmol/l) s uperfusing solution increased the cell diameter and the pretreatment w ith DIDS or with niflumic acid significantly potentiated the above eff ect of hyposmotic superfusion. These results suggest that volume-sensi tive outwardly rectifying chloride current (I-Cl) is present in guinea -pig gastric myocyte and the I-Cl may play a role in smooth muscle cel l volume regulation.