Role of Ca++ gradient in functional dilatation in the microvessels of rat skeletal muscle.

ABSTRACT

During skeletal muscle contraction functional dilatation (FD) is a well established phenomenon, which is usually linked to the accumulation of various vasodilator metabolites. The present study aimed to establish the role of calcium ions (Ca++) in the functional dilatation of skeletal muscle microvessels especially during single & few twitches. The FD was studied in urethane anaesthetized rats whose spinotrapezius muscle was prepared for intravital microscopy. After stimulating the muscle with few twitch (1 & 3 Hz) and tetanic frequency (40 Hz), muscle contracted and showed dilatation. However the dilator response was quickest (1 Hz 10 +/- 0.40, 3 Hz 02 +/- 0.47 sec and 40 Hz 02 +/- 0.10 sec) and maximum in magnitude (1 Hz 25 +/- 0.30%, 3 Hz 35 +/- 0.49% and 40 Hz 55 +/- 0.39%) in terminal arteriole and with tetanic frequency. Calcium channel blockade by Diltiazem abolished the FD response except for tetanic stimulation contraction. Findings suggested possible involvement of Ca++ movement in functional dilatation which was initiated by passive efflux of Ca++ from smooth muscle of vessel and then maintained during higher frequency stimulation by release of local metabolities.