Excitatory effect of Cd2+ on cat adrenal chromaffin cells.
To understand the mechanism(s) underlying the Cd2+- and Co2+-induced increases in the cytosolic free Ca2+ concentration ([Ca]i) in cat adrenal chromaffin cells, we used nystatin-perforated patch recording method and fura-2 microfluorometry. Under the current-clamp conditions, the external application of 5x10(-7) M Cd2+ slowly depolarized the cells resulting in the bursting of action potentials. Under the voltage-clamp conditions, Cd2+ evoked a slow inward current accompanied by a decrease of K+ conductance at a holding potential of -40 mV, and Co2+ mimicked Cd2+ action. In some cells (16%), Cd2+ evoked an additional rapid transient outward current associated with an increased K+ conductance and a successive slow inward current. The Cd2+-induced inward current was activated in a concentration-dependent manner with a half-maximum concentration of 9.3x10(-8) M. The Cd2+- and Co2+-induced [Ca]i increases measured with fura-2 microfluorometry were maximal at 10(-6) and 10(-5) M, respectively, and the higher concentrations of both cations caused the smaller responses. Additional transient increase in [Ca]i was often evoked upon the removal of relatively higher concentrations of these metals. It was concluded that the Cd2+-induced membrane depolarization due to the decrease in K+ conductances evoked the bursting firings resulting in the increase in [Ca]i, and consequently might stimulate the catecholamine secretion.
Sorimachi
M
M
Department of Physiology, Kagoshima University, Faculty of Medicine, Kagoshima, 890-8520, Japan. ciliary@med2.kufm.kagoshima-u.ac.jp
Yamagami
K
K
Rhee
J S
JS
Ishibashi
H
H
Akaike
N
N
D000818:Animals; D002104:Cadmium / Q000494:pharmacology*; D002415:Cats; D019439:Chromaffin Cells / Q000187:drug effects*; D003035:Cobalt / Q000494:pharmacology*; D003592:Cytophotometry; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D016257:Fura-2; D066298:In Vitro Techniques; D007476:Ionophores / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009761:Nystatin / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D019284:Thapsigargin / Q000494:pharmacology
D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D007476:Ionophores; D002104:Cadmium; D009761:Nystatin; D003035:Cobalt; D019284:Thapsigargin; D016257:Fura-2