AJP - Regulatory, Integrative and Comparative Physiology, Vol 266, Issue 3 651-R657, Copyright © 1994 by American Physiological Society

ARTICLES

Lack of effect of ouabain on calcium homeostasis in rat platelets: comparative study with human platelets

T. Oshima, T. Ishida, H. Matsuura, M. Ishida, K. Ishibashi, R. Ozono, M. Watanabe, G. Kajiyama and M. Kanbe
Department of Clinical Laboratory Medicine, Hiroshima University School of Medicine, Japan.

The precise mechanisms of Ca2+ handling in rat platelets are not fully understood. We sought to determine whether rat platelets possess a Na(+)-Ca2+ exchanger. First, we investigated the time course of the effect of ouabain (10(-4) M) on cytosolic sodium concentration ([Na+]i) and Ca2+ homeostasis in platelets from Wistar rats in comparison with those from humans. Ouabain increased platelet [Na+]i in both rat and human platelets. Whereas ouabain induced a time-dependent increase in basal and thrombin-stimulated (0.3 units/ml) cytosolic calcium concentration ([Ca2+]i) in human platelets, no change was found in rat platelets. Furthermore, 90-min pretreatment of rat platelets with ouabain did not affect the [Ca2+]i response to thrombin (0.1-1.0 units/ml) or a maximal dose of ionomycin (5 microM). Also the decline in [Ca2+]i after the peak response evoked by these agonists in the absence of extracellular Ca2+ was not changed by ouabain pretreatment. Similarly, replacement of extracellular Na+ had no influence on any of these determinations. Thus decreasing the plasma membrane Na+ gradient did not affect basal [Ca2+]i, thrombin-induced mobilization of Ca2+ from intracellular stores, internal Ca2+ discharge capacity, or Ca2+ extrusion from cytosol of rat platelets. In contrast to human platelets, a Na(+)-Ca2+ exchange mechanism does not appear to play a significant role in Ca2+ homeostasis of rat platelets.

This article has been cited by other articles:

				H. Hiraga, T. Oshima, M. Yoshimura, H. Matsuura, and G. Kajiyama Abnormal platelet Ca2+ handling accompanied by increased cytosolic free Mg2+ in essential hypertension Am J Physiol Regulatory Integrative Comp Physiol, August 1, 1998; 275(2): R574 - R579. [Abstract] [Full Text] [PDF]

				M. Yoshimura, T. Oshima, H. Hiraga, Y. Nakano, H. Matsuura, T. Yamagata, N. Shiode, M. Kato, M. Kambe, and G. Kajiyama Increased cytosolic free Mg2+ and Ca2+ in platelets of patients with vasospastic angina Am J Physiol Regulatory Integrative Comp Physiol, February 1, 1998; 274(2): R548 - R554. [Abstract] [Full Text] [PDF]

				M. Ishida, T. Ishida, N. Ono, H. Matsuura, M. Watanabe, G. Kajiyama, M. Kambe, and T. Oshima Effects of Insulin on Calcium Metabolism and Platelet Aggregation Hypertension, August 1, 1996; 28(2): 209 - 212. [Abstract] [Full Text]

				N. Ono, T. Oshima, M. Ishida, T. Ishida, H. Matsuura, M. Kambe, and G. Kajiyama Platelet Ca2+ Is Not Increased in Stroke-Prone Spontaneously Hypertensive Rats : Comparative Study With Spontaneously Hypertensive Rats Hypertension, June 1, 1996; 27(6): 1312 - 1317. [Abstract] [Full Text]