Signal transduction for activation of Ca-dependent Cl channel in tracheal smooth muscle cells of the guinea-pig

Abstract

When a single smooth muscle cell isolated from guinea-pig trachea was depolarized or treated with caffeine under whole cell voltage-clamp, Ca-dependent K and Cl currents (IK-Ca and ICI-Ca) were elicited. Spontaneous transient outward and inward currents (STOC and STIC) were simultaneously recorded at holding potential of -40 mV. These were IK-Ca and ICI-Ca, respectively, which were activated by spontaneous Ca release from local store sites. The time-course of activation and deactivation of these ICI-Cas was several times slower than that of corresponding IK-Cas. The slower time-course of ICI-Ca activation may be due to the involvement of signal transduction and phosphorylation of channel protein, whereas Ca-dependent K channel activity is directly regulated by [Ca2+]i. Alternatively, the Cl channel may also be directly regulated by [Ca2+]i but has much slower kinetics than the K channel. Pharmacological analyses suggest that calmodulin and related signal transduction may not be involved in the activation of ICI-Ca. It was also unlikely that activation of protein kinase A, G or C or tyrosine-kinase is primarily responsible for the channel activation. Single CI channel activity was recorded using cell-attached patch clamp from cells which were skinned by β-escin. The Cl channel had low density and large conductance (370 pS) and its activity strongly depended upon [Ca2+]i. Cytosolic large molecules may be essential for the channel activation since the activity did not run down significantly in skinned cells, whereas it did in excised patches. © 1995, The Japanese Pharmacological Society. All rights reserved.