Ca2+ Release and Heat Production by the Endoplasmic Reticulum Ca2+-ATPase of Blood Platelets

doi:10.1074/jbc.274.40.28344

Ca²⁺ Release and Heat Production by the Endoplasmic Reticulum Ca²⁺-ATPase of Blood Platelets

EFFECT OF THE PLATELET ACTIVATING FACTOR*

From the Instituto de Ciências Biomédicas, Departamento de Bioquı́mica Médica, Universidade Federal do Rio de Janeiro, Cidade Universitária, Rio de Janeiro 21941-590,-Brasil

Abstract

Different sarco/endoplasmic reticulum Ca²⁺-ATPases isoforms are found in blood platelets and in skeletal muscle. The amount of heat produced during ATP hydrolysis by vesicles derived from the endoplasmic reticulum of blood platelets was the same in the absence and presence of a transmembrane Ca²⁺ gradient. Addition of platelets activating factor (PAF) to the medium promoted both a Ca²⁺ efflux that was arrested by thapsigargin and an increase of the yield of heat produced during ATP hydrolysis. The calorimetric enthalpy of ATP hydrolysis (ΔH ^cal) measured during Ca²⁺transport varied between −10 and −12 kcal/mol without PAF and between −20 and −24 kcal/mol with 4 μm PAF. Different from platelets, in skeletal muscle vesicles a thapsigargin-sensitive Ca²⁺ efflux and a high heat production during ATP hydrolysis were measured without PAF and the ΔH ^cal varied between −10 and −12 kcal/mol in the absence of Ca²⁺ and between −22 up to −32 kcal/mol after formation of a transmembrane Ca²⁺ gradient. PAF did not enhance the rate of thapsigargin-sensitive Ca²⁺ efflux nor increase the yield of heat produced during ATP hydrolysis. These findings indicate that the platelets of Ca²⁺-ATPase isoforms are only able to convert osmotic energy into heat in the presence of PAF.

Footnotes

↵* This work was supported in part by grants from PRONEX, Financiadora de Estudos e Projetos (FINEP), and the Conselho Nacional de Desenvolvimento Cientı́fico e Tecnológico (CNPq).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵‡ Recipient of a fellowship from CNPq.
↵§ To whom correspondence should be addressed: Instituto de Ciências Biomédicas, Departamento de Bioquı́mica Médica, Universidade Federal do Rio de Janeiro, Cidade Universitária, RJ 21941-590, Brasil. Fax: 55-21-270-8647; E-mail: demeis@server.bioqmed.ufrj.br.
Abbreviations:

SERCA

sarco/endoplasmic reticulum Ca²⁺-ATPase

PAF

platelet activating factor

MOPS

4-morpholinepropanesulfonic acid
- Received June 8, 1999.
- Revision received July 21, 1999.
The American Society for Biochemistry and Molecular Biology, Inc.