Volume-activated chloride currents in interstitial cells of Cajal
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abstract
Interstitial cells of Cajal (ICC) undergo marked morphological changes on contraction of the musculature, making it essential to understand properties of mechanosensitive ion channels. The whole cell patch-clamp technique was used to identify and to characterize volume-activated Cl− currents in ICC cultured through the explant technique. Hypotonic solutions (≈210 mosM) activated an outwardly rectifying current, which reversed near the equilibrium potential for Cl−. Time-dependent inactivation occurred only at pulse potentials of +80 mV, with a time constant of 478 ± 182 ms. The degree of outward rectification was calculated using a rectification index, the ratio between the slope conductances of +65 and −55 mV, which was 13.9 ± 1.5 at 76 mM initial extracellular Cl− concentration. The sequence of relative anion permeability of the outwardly rectifying Cl− channel was I− > Cl− > aspartate−. The chloride channel blockers, DIDS and 5-nitro-2-(3-phenlypropl-amino)benzoic acid, caused a voltage-dependent block of the outwardly rectifying Cl− current, inhibition occurring primarily at depolarized potentials. On exposure to hypotonic solution, the slope conductance significantly increased at the resting membrane potential (−70 mV) from 1.2 ± 0.2 to 2.0 ± 0.4 nS and at the slow-wave plateau potential (−35 mV) from 2.1 ± 0.3 to 5.0 ± 1.0 nS. The current was constitutively active in ICC and contributed to the resting membrane potential and excitability at the slow-wave plateau. In conclusion, swelling or volume change will depolarize ICC through activation of outwardly rectifying chloride channels, thereby increasing cell excitability.
