Immortalized GnRH Neurons Express Large-Conductance Calcium-Activated Potassium Channels

Publisher Website
Google Scholar
Abstract
The expression and function of large-conductance Ca2+-activated K+ (BK) channels in the GT1-7 line of immortalized gonadotropin-releasing hormone (GnRH) neurons was investigated. Ionic currents were recorded using the patch-clamp technique, cytoplasmic free Ca2+ concentration ([Ca2+]i) was monitored using the fluorescent indicator, fura-2, and GnRH secretion was measured by radioimmunoassay. In cell-attached and inside-out patch-clamp recordings, K+ channels with a single-channel conductance of ∼200 pS were detected. Depolarizing the patch increased the unitary current size and the open probability. In perforated-patch recordings, depolarizing pulses (50 ms) to potentials of –10 to +60 mV from a holding potential of –90 mV elicited outward current with early transient and sustained components. The transient current peaked 2–10 ms after the beginning of each pulse and increased in a voltage-dependent manner. This current was: (1) unaffected by the small-conductance Ca2+-activated K+ channel blocker, apamin (100 nM); (2) reduced by the BK channel blocker, charybdotoxin (5 nM); (3) abolished by the Ca2+ channel blocker, CdCl2 (25 µM), and (4) prolonged by the endoplasmic reticu-lum Ca2+-ATPase inhibitor, thapsigargin (1 µM). Based on the single-channel and whole-cell conductances, the number of channels per patch, the patch area, and the surface area of the cell, each GT1-7 cell contains 30–60 BK channels. The functional role of BK channels in GT1-7 cells was evaluated by measuring the effect of charybdotoxin (100 nM) on basal [Ca2+]i and GnRH secretion, as well as on the [Ca2+]i and GnRH secretory responses to γ-aminobutyric acid (GABA, 100 µM), an excitatory neurotransmitter in this system. Charybdotoxin had no effect on basal [Ca2+]i or GnRH secretion, or on the GABA-evoked [Ca2+]i and GnRH secretory responses. These results indicate that GT1-7 cells express BK channels; however, the physiological role of BK channels in GT1-7 cells remains elusive.

This publication has 0 references indexed in Scilit: