Anomalous increase of Ca2+ current by high concentration K+ stimulation in whole cell clamped GH3 cells.
We examined the effect of high concentration K+ (50 mM K+) stimulation to neurosecretory GH3 cells under voltage clamp control and unexpectedly found a considerable increase in the inward current evoked by depolarizing pulses. This augmented current was present in Na+-free solution containing Ca2+, tetraethylammonium+ and tetrodotoxin and showed similarity in its voltage dependence to the Ca+ channel current in the control (5 mM K+) solution. The augmented current was significantly reduced by Ca2+ channel blockers, Co2+ (5 mM) and nifedipine (2.5 microM), and was increased by the raise of external Ca2+ concentration. Correspondingly, Quin-2 experiments in GH3 cells showed that the rise in cytosolic free Ca2+ concentration in response to high K+ stimulation was suppressed by the same concentration of nifedipine. These data suggest that, in addition to its depolarizing effect, high K+ may modify voltage-sensitive Ca2+ channels such that they exhibit increased permeability although their voltage dependence of activation and pharmacological sensitivity remain largely unchanged.
Suzuki
N
N
Department of Physiology, Kitasato University School of Medicine, Kanagawa, Japan.
Yoshioka
T
T
Okano
Y
Y
Nozawa
Y
Y
Kano
M
M
D000818:Animals; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology*; D003035:Cobalt / Q000494:pharmacology; D004553:Electric Conductivity; D008564:Membrane Potentials / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology*; D051381:Rats; D014407:Tumor Cells, Cultured
D015220:Calcium Channels; D003035:Cobalt; D011188:Potassium; D002118:Calcium