The dilation of arterioles in frog submaxillaris muscle caused by visible light.

Transillumination of submaxillaris muscle with incandenscent lamp led to arteriolar dilation if the illuminance exceeded 1-2 x 10(3) lux or reached the time-mean value of 3 x 10(4) lux when a flash lamp was used (pulse duration 10 microseconds, repetition rate 50 s-1). The temperature increase within a light spot on the muscle did not exceed 0.1 degrees C, visible light being the only reason of the dilation of arterioles. At 6.3 x 10(4) lux (incandescent lamp, green filter) the latency of dilation in 64% of trials was less than 20 s while the average increase in diameter amounted to 69 +/- 5.0% within 2 to 4 min of radiation. In the muscle with intact innervation, dilation of arterioles slower. We supposed that due to the limitation of Bunsen-Roscoe law powerful, but short light pulses may fail to induce a photochemical reaction and the ensuring dilation. Indeed, repetitive flashes (10 microseconds, 30 s-1) producing the time-mean illuminance of 2 x 10(4) lux caused neither dilation of arterioles nor suppression of their vasomotion. The light-induced dilation allowed the conversion of closed and plasmatic arterioles into the vessels filled with moving blood. Photodilation of frog muscle arterioles may be employed to investigate a number of basic properties of their smooth muscles.