Clustering of protein kinase A-dependent CFTR chloride channels in the sarcolemma of guinea-pig ventricular myocytes

Cardiac myocytes express protein kinase A-dependent Cl- (ClPKA) channels that are thought to represent cardiac expression of CFTR. In the present study, the [`]Smart' patch clamp technique was used to investigate the distribution of ClPKA channels at the cell surface of isolated guinea-pig ventricular myocytes. Imaging the cell surface using scanning ion conductance microscopy allowed the identification of the mouths to t-tubules and lateral z-grooves with a spacing of 1.86 [mu]m. Cell-attached patch clamp recordings were made from specified locations within the imaged area. Perfusion of the cells with an activating cocktail of isoprenaline (5 [mu]M), forskolin (10 [mu]M) and isobutylmethylxanthine (50 [mu]M) activated large, noisy anion-selective currents in which unitary channel currents could not be identified. Currents were recorded both from within z-grooves and in the inter-groove region but not at the mouths of t-tubules. Power spectral and noise analyses indicated the involvement of 13.5 pS channels occurring in clusters of >50 channels. Channel activity was lost on excision of the patch from the cell but could be recovered in inside-out excised patches by application of the catalytic subunit of PKA. These results suggest that CFTR ClPKA channels occur in clusters in the sarcolemma of guinea-pig ventricular myocytes; there was no evidence of a heterogeneous distribution of clusters between the z-grooves and the inter-groove region.