Nicotinic acetylcholine receptors in porcine hypophyseal intermediate lobe cells.

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RESUMO

1. Acetylcholine (ACh) was found to depolarize isolated porcine intermediate lobe cells maintained in primary cells culture. We investigated the ACh-induced responses in both whole-cell and cell-attached configurations of the patch-clamp technique. 2. From noise analysis of ACh-evoked whole-cell currents, we estimated an elementary conductance of 20 pS and a channel open duration of about 1.7 ms at -60 mV. From single-channel recordings, we obtained a slope conductance of 26 pS and a mean open time of 1.8 ms at membrane potentials between -60 and -80 mV. 3. ACh-evoked responses were blocked by d-tubocurarine (d-TC), hexamethonium and mecamylamine, but were insensitive to alpha-bungarotoxin. These characteristics define a neuronal type of nicotinic receptors. 4. The whole-cell current induced by ACh showed a strong inward rectification with no outward current being obtained. This phenomenon was observed when the intracellular ion is either sodium or caesium, and even when Ca2+ and Mg2+ were totally removed from the intracellular medium. 5. ACh-gated channels in intermediate lobe cells were cation selective and were permeable to Na+ and Cs+. In Ca2(+)-free extracellular solution, single-channel conductances were much larger (46 pS) than in the presence of 2 mM-Ca2+ (26 pS). 6. The possibility of an excitatory cholinergic control of intermediate lobe cells is discussed.

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