Frequency and pattern dependence of adrenergic and purinergic vasoconstriction in rat skeletal muscle arteries

Abstract

Sympathetic nerves fire in bursts followed by brief periods of quiescence. Periods of quiescence may be a valuable part of coding for different neurotransmitters. We compared adrenergic- and non-adrenergic-mediated vasoconstriction with repeating burst patterns versus constant frequency stimulation. Seventeen rats were killed, and the femoral arteries dissected out and mounted in organ tissue baths at 37 degrees C and pH 7.4. Field stimulation was applied to artery rings from five rats at constant frequencies of 2-6 Hz for 144 impulses. In 12 rats, artery rings were stimulated with two burst pattern protocols consisting of repeating pairs, triplets, quadruplets or sextuplets performed using either 8 or 30 Hz as the instantaneous frequency for a total of 144 impulses. All protocols were repeated with the P2 purinergic antagonist pyridoxal-phosphate-6-azophenyl-2'4'-disulphonic acid (PPADs; 0.42 m) or the alpha(1)-antagonist prazosin (1.59 microM). Tension was decreased by the addition of the P2 antagonist PPADs (P < 0.05). Prazosin abolished tension at all constant frequencies (P < 0.05). P2 and alpha(1)-antagonism decreased tension with 8 and 30 Hz burst pattern field stimulation. However, the magnitude of decrease in tension with prazosin was less with burst patterns compared to the same average constant frequencies (P < 0.05). It appears that P2X receptors and alpha(1)-receptors in the femoral artery are sensitive to frequency and patterns of electrical stimulation.