Alterations in Transmembrane Potential of Adenohypophysial Cells in Elevated Potassium and Calcium-Free Media

Abstract

Measurements of transmembrane potential (V_m) were obtained in 117 cells from the adenohypophyses of 14 rats in vitro when the glands were superfused with Krebs—Ringer bicarbonate (KRB). The mean V_m was -12.0 mV ±.4 SE, in agreement with previous in vitro findings. No positive V_m's were observed. V_m and R (resistance) of individual cells were recorded while the superfusion fluid was changed. A depolarization of the cells of the adenohypophysis was demonstrated in an elevated [K⁺]_o medium (5x[K⁺]₀ KRB). This depolarization appeared to be dependent upon the calcium ion concentration of the medium. The percent depolarization averaged 37.3% ± 3.0 SE for 23 cells in 5x[K⁺]₀ –normal [Ca⁺⁺]₀ KRB, but was significantly smaller (p less than 0.05) in 5x[K⁺]_o– [Ca⁺⁺]₀ free KRB, averaging 28%±2.3 SE for 19 cells. A small but significant depolarization (24.5% ± 3.5 SE, 20 cells) was demonstrated when the normal medium (KRB) was replaced with a calcium—free medium (0[Ca⁺⁺]_o KRB). No change in membrane resistance from control values was observed in either elevated [K⁺]_o or [Ca⁺⁺]_o free media. Depolarization is thus not tightly coupled to secretion for it could occur under conditions known to inhibit secretion. (Endocrinology92: 1084, 1973)