Characterization of K+ and Ca2+ ionic currents in glomerulosa cells from human adrenal glands.

Abstract

Ionic currents of primary cultured glomerulosa cells from human adrenal glands were studied with the patch-clamp technique. Two types of outward K+ currents and two types of inward Ca2+ currents were described. The transient outward K+ current activated at potential positive to -40 mV and demonstrated a marked time-dependent inactivation. It was blocked by 4-aminopyridine but not tetraethylammonium. A second type of outward current activated rapidly at the depolarization onset and then increased slowly with no time-dependent inactivation. The transient inward T-type Ca2+ current was activated for potential positive to -60 mV with a maximal current amplitude at -30 mV and zero current voltage at +40 mV; it was completely inactivated for membrane potential positive to -40 mV. The pharmacological studies of the T-type channel showed that Ni2+ was a potent blocker but that the channel was not sensitive to dihydropyridine. The long-lasting inward Ca2+ current was activated for potentials positive to -20 mV with a maximum current amplitude at +70 mV. This current was increased by the agonist Bay K 8644 and blocked by the antagonist nifedipine; in addition, it was blocked by Cd2+ but less sensitive to Ni2+. This study revealed that glomerulosa cells from human adrenal demonstrated the presence of K+ and Ca2+ currents similar to those found in rat and bovine cells. Moreover, the main stimuli of aldosterone secretion, ACTH and angiotensin II, induce an increase in aldosterone secretion which is inhibited in a Ca(2+)-free external medium.

Role of Ca2+ in the action of adrenocorticotropin in cultured human adrenal glomerulosa cells.

“…We have previously shown that, in human glomerulosa cells, NiCl 2 and nifedipine specifically blocked Ca 2ϩ channels (22). Results from Fig.…”

“…As previously described by our group, human glomerulosa possess both K ϩ and Ca 2ϩ currents (22). T-and L-type Ca 2ϩ currents were studied after blocking outward currents and using a double pulse protocol as described previously (22).…”

“…Ionic currents recordings were obtained using the whole-cell configuration of the patch clamp method (22)(23)(24) in the voltage clamp configuration. Patch electrodes were made from Pyrex glass (7740; Corning Glass Works, Corning, NY) with a resistance ranging between 4-8 M ⍀ .…”

“…Even its role in hormone secretion is questioned since, in some studies, the addition of verapamil markedly inhibited corticosteroidogenesis in response to ACTH (20), while in others these Ca 2 ϩ channel blockers inhibited the effect of Ang II and potassium, with little effect on ACTH response (21). Recent data from our laboratory have shown that K ϩ and Ca 2 ϩ channels are present in human glomerulosa cells (22). In rat cells, similar ionic channels were previously described to be modulated by ACTH (23,24).…”

60 YEARS OF POMC: Adrenal and extra-adrenal functions of ACTH

“…Such observations could explain that, in humans, aldosterone secretion is more sensitive to low doses of ACTH(1-24) than the secretion of cortisol or DHEA (Daidoh et al 1995), especially in conditions of sodium depletion (Rayfield et al 1973, Kem et al 1975, Nicholls et al 1975. In rat and human ZG cells, binding of ACTH to its receptor induces a rapid membrane depolarization, in part due to blockade of K + channels (Payet et al 1987(Payet et al , 1994. Simultaneously, depolarization transiently abolishes T-channel activity (Durroux et al 1991) and increases the amplitude of the L-type current, through a cAMP-dependent or a PKA-dependent phosphorylation of these L-type channels (Durroux et al 1991).…”