Mastoparan stimulates exocytosis at a Ca(2+)-independent late site in stimulus-secretion coupling. Studies with the RINm5F beta-cell line

Komatsu, Mitsuhisa, McDermott, Alison, Gillison, Susan and Sharp, Geoffrey (1993) Mastoparan stimulates exocytosis at a Ca(2+)-independent late site in stimulus-secretion coupling. Studies with the RINm5F beta-cell line. Journal of Biological Chemistry, 268 (31). pp. 23297-23306. ISSN 1083-351X

Full text not available from this repository. (Request a copy)

Abstract

Mastoparan, a tetradecapeptide from wasp venom, stimulated exocytosis in a concentration-dependent manner, which was enhanced by pertussis toxin pre-treatment, in the insulin secreting beta-cell line RINm5F. Mastoparan (3-20 microM) also elevated cytosolic free calcium concentration ([Ca2+]i), a rise that was not attenuated by nitrendipine. Divalent cation-free Krebs-Ringer bicarbonate (KRB) medium with 0.1 mM EGTA nullified the mastoparan-induced increase in [Ca2+]i, suggesting that the peptide increased Ca2+ influx but not through the L-type voltage-dependent Ca2+ channel. Depletion of the intracellular Ca2+ pool did not affect the mastoparan-induced elevation of [Ca2+]i. Remarkably, in divalent cation-free KRB medium with 0.1 mM EGTA and 2 microM thapsigargin in which mastoparan reduced [Ca2+]i, the mastoparan-stimulated insulin release was similar to that in normal Ca(2+)-containing KRB medium. Inhibitors of protein kinase C, such as bisindolylmaleimide, staurosporine, and 1-O-hexadecyl-2-O-methyl-rac-glycerol did not suppress the mastoparan-stimulated insulin release. Mastoparan at 10-20 microM did not increase cellular cAMP levels, nor did mastoparan at 5-10 microM affect [3H]arachidonic acid release. In conclusion, although mastoparan increased [Ca2+]i, this increase was not involved in the stimulation of insulin release. Rather, the data suggest that mastoparan directly stimulates exocytosis in a Ca(2+)-independent manner. As GTP-binding proteins (G proteins) are thought to be involved in the process of exocytosis and as mastoparan is known to exert at least some of its effects by activation of G proteins, an action of mastoparan to activate the putative stimulatory Ge (exocytosis) protein is likely.

Item Type:	Article
Subjects:	B200 Pharmacology, Toxicology and Pharmacy
Department:	Faculties > Health and Life Sciences > Applied Sciences
Depositing User:	Becky Skoyles
Date Deposited:	24 May 2017 15:12
Last Modified:	12 Oct 2019 17:29
URI:	http://nrl.northumbria.ac.uk/id/eprint/30848

Downloads