PLATELET CALCIUM HANDLING IN SPONTANEOUSLY HYPERTENSIVE RATS AND IN 3STRAINS OF NORMOTENSIVE RATS

Objectives: Abnormalities in platelet calcium handling have been repor ted in spontaneously hypertensive rats (SHR) compared with Wistar-Kyot o (WKY) rats. Furthermore, several reports have indicated that WKY rat s differ from both SHR and Wistar rats. The objectives of the present study were to investigate platelet calcium handling in three normotens ive stains and in SHR, and to confirm the abnormal calcium mobilizatio n in SHR. Design and methods: We compared calcium handling in fura-2-l oaded platelets of SHR, Wistar, Sprague-Dawley (SD) and WKY rats. Resu lts: The basal cytosolic free Ca2+ concentration in platelets was sign ificantly higher in SHR and significantly lower in SD rats than in the other strains. The intracellular Ca2+ response to thrombin in the pre sence of extracellular Ca2+ was greater in SHR than in the three normo tensive strains. The thrombin-induced intracellular Ca2+ rise in the a bsence of extracellular Ca2+ was also greater in SHR and lower in SD r ats than in the other strains. However, there was no significant diffe rence among SHR, WKY and Wistar rats at higher doses of thrombin. The intracellular ionomycin-released calcium fraction, which may indicate the size of intracellular calcium stores, was similar in SHR, WKY and Wistar rats, and was greater than in SD rats. No difference was detect ed between WKY and Wistar rats in resting and peak agonist-evoked intr acellular Ca2+ concentrations. Conclusions: These results show that ca lcium handling in WKY rats is similar to that in Wistar rats with resp ect to platelet calcium metabolism and confirm the abnormality in SHR. Furthermore, the enhanced intracellular Ca2+ response to thrombin in SHR was not dependent on the size of ionomycin-released Ca2+ stores. I n addition, substantial differences in platelet calcium handling may o ccur even among normotensive strains if the strains are not related.