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Patch-clamp analysis of voltage-gated currents in intermediate lobe cells from rat pituitary thin slices

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Abstract

Ionic currents of hypophyseal intermediate lobe cells were studied using a thin-slice preparation of the rat pituitary in conjunction with conventional and perforated whole-cell patch-clamp recording techniques. A majority (89%) of the cells studied generated Na+, Ca2+ and K+ currents upon depolarizing voltage steps and responded to bath application of γ-aminobutyric acid (GABA; 20–50 μM) with inward currents (in symmetrical chloride, holding potential −80 mV). A small percentage of cells (11%) did not display inward membrane currents upon depolarization and was unresponsive to GABA. In the first type of cells, Ca2+ and K+ currents were further studied in isolation. Ca2+ tail currents showed a biphasic time course upon repolarization, with time constants and amplitudes of 2.07±0.29 ms, 123±22 pA (for the slowly deactivating component) and 0.14±0.06 ms, 437±33 pA (for the fast-deactivating component; means±SD of n=4 cells). Slowly and fast-deactivating conductances were half-maximally activated at around −10 mV and +10 mV respectively. Depolarizing voltage steps elicited two types of K+ current, which were separated using a prepulse protocol. A fast-activating, transient component showed half-maximal steadystate inactivation between −65 mV and −45 mV depending on the divalent cation composition of the external solution. Its decay was fitted by single-exponential functions with time constants of 36±11 ms and 3.9±0.9 ms at −20 mV and +40 mV respectively (mean±SD; n=4 cells). Whereas the peak current amplitudes of the transient K+ current component remained stable, the amplitude of the second, delayed component increased progressively throughout the course of whole-cell experiments. In cells recorded with the perforated whole-cell technique, bath application of dopamine (10 nM−1 μM) induced large hyperpolarizations from a spontaneous membrane potential of −40 mV, but did not consistently affect the amplitude of the voltage-gated K+ conductances. These data are compared to previous studies using other preparations of the intermediate lobe, and differences are discussed, thus helping to extend our knowledge of electrical excitability of hypophyseal cells.

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Correspondence to J. López-Barneo.

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Schneggenburger, R., López-Barneo, J. Patch-clamp analysis of voltage-gated currents in intermediate lobe cells from rat pituitary thin slices. Pflügers Arch 420, 302–312 (1992). https://doi.org/10.1007/BF00374463

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Key words

  • Voltage-gated currents
  • Intermediate lobe
  • Hypophysis
  • Thin-slices
  • Patch clamp