Effects of funnel web spider toxin on Ca2+ currents in neurohypophysial terminals.
Funnel web spider toxin (FTX) is reportedly a specific blocker of P-type Ca2+ channels. The effects of FTX on the Ca2+ currents of isolated neurohypophysial nerve terminals of the rat were investigated using the 'whole-cell' patch-clamp technique. Both the transient and long-lasting Ca2+ current components were maximally elicited by depolarization from a holding potential equal to the normal terminal resting potential (-90 mV). Externally applied FTX inhibited the high-voltage-threshold, transient component of the Ca2+ current in a concentration-dependent manner, with a half-maximal inhibition at a dilution of approximately 1:10000. FTX also shifted the peak current of the I-V relationship by +10 mV. The long-lasting Ca2+ current component, which is sensitive to L-type Ca2+ channel blockers, was insensitive to FTX. The transient current, which is sensitive to omega-conotoxin GVIA, was completely blocked by FTX. These results suggest that there could be a novel, inactivating Ca2+ channel in the rat neurohypophysial terminals which is affected by both N-type and P-type Ca2+ channel blockers.
Wang
G
G
Worcester Foundation for Experimental Biology, Shrewsbury, MA 01545.
Lemos
J R
JR
D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D044182:Benzylisoquinolines; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D004095:Dihydropyridines / Q000494:pharmacology; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D008978:Mollusk Venoms / Q000494:pharmacology; D009411:Nerve Endings / Q000187:drug effects*; D010455:Peptides / Q000494:pharmacology; D010904:Pituitary Gland, Posterior / Q000187:drug effects* / Q000294:innervation; D011073:Polyamines / Q000494:pharmacology*; D051381:Rats; D013111:Spider Venoms / Q000494:pharmacology*; D020866:omega-Conotoxin GVIA
D000470:Alkaloids; D044182:Benzylisoquinolines; D002121:Calcium Channel Blockers; D004095:Dihydropyridines; C071920:FTX, spider toxin; D008978:Mollusk Venoms; D010455:Peptides; D011073:Polyamines; D013111:Spider Venoms; C009438:tetrandrine; C038806:1,4-dihydropyridine; D020866:omega-Conotoxin GVIA