Effects of Ca2+ channel antagonists on chromaffin cell death and cytosolic Ca2+ oscillations induced by veratridine.
Exposure of bovine chromaffin cells to 30 microM veratridine for 24 h led to 70-80% cell death as reflected by phase contrast microscopy, trypan blue exclusion, lactate dehydrogenase (LDH) release and cell catecholamine contents. Na+ deprivation, Ca2+ deletion or tetrodotoxin (5 microM) prevented the veratridine-induced cell damage. Nimodipine and verapamil, but not omega-conotoxin GVIA afforded 20-30% protection. Flunarizine protected the cells by 80% and R56865 by 60%. Stimulation of fura-2-loaded single bovine chromaffin cells with 30 microM of 1,1-dimethyl-4-phenylpiperazinium (DMPP) or 59 mM K+ caused fast increases in cytosolic Ca2+ concentrations, ([Ca2+]i). The [Ca2+]i rose from 0.1 to peaks of 1.9 microM, which quickly declined to near basal levels with a t1/2 of around 30 s. In spite of sustained stimulation with these two depolarizing agents, the [Ca2+]i remained low and did not undergo oscillations. In contrast, veratridine (30 microM) caused large and frequent oscillatory changes in the [Ca2+]i which were long-lasting and did not disappear even 30 min after washing out the toxin. The [Ca2+]i oscillations were reversibly suppressed by Na+ or Ca2+ removal and by 5 microM tetrodotoxin. Selective L-type Ca2+ channel blockers (10 microM nimodipine or verapamil) or N-type Ca2+ channel blockers (1 microM omega-conotoxin GVIA) did not affect the [Ca2+]i oscillations. In contrast, flunarizine or R56865 (10 microM each) suppressed the oscillations of [Ca2+]i. The results demonstrate that bovine chromaffin cells have the necessary machinery to develop prolonged and repetitive [Ca2+]i oscillations in the presence of veratridine; however, 'physiological' depolarizing stimuli did not cause oscillations.(ABSTRACT TRUNCATED AT 250 WORDS)
Maroto
R
R
Departamento de Farmacología, Facultad de Medicina, Universidad Autónoma de Madrid, Spain.
De la Fuente
M T
MT
Artalejo
A R
AR
Abad
F
F
López
M G
MG
García-Sancho
J
J
García
A G
AG
D000313:Adrenal Medulla / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D002417:Cattle; D016923:Cell Death / Q000187:drug effects; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D004246:Dimethylphenylpiperazinium Iodide / Q000494:pharmacology; D016257:Fura-2; D011188:Potassium / Q000494:pharmacology; D011978:Receptors, Nicotinic / Q000187:drug effects; D012964:Sodium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology*
D002121:Calcium Channel Blockers; D011978:Receptors, Nicotinic; D013779:Tetrodotoxin; D004246:Dimethylphenylpiperazinium Iodide; D014701:Veratridine; D012964:Sodium; D011188:Potassium; D002118:Calcium; D016257:Fura-2