Sympathetically evoked Ca²⁺ signaling in arterial smooth muscle

The sympathetic nervous system plays an essential role in the control of total peripheral vascular resistance and blood flow, by controlling the contraction of small arteries. Perivascular sympathetic nerves release ATP, norepinephrine (NE) and neuropeptide Y. This review summarizes our knowledge of the intracellular Ca²⁺ signals that are activated by ATP and NE, acting respectively on P2X₁ and α₁-adrenoceptors in arterial smooth muscle. Each neurotransmitter produces a unique type of post-synaptic Ca²⁺ signal and associated contraction. The neural release of ATP and NE is thought to vary markedly with the pattern of nerve activity, probably reflecting both pre- and post-synaptic mechanisms. Finally, we show that Ca²⁺ signaling during neurogenic contractions activated by trains of sympathetic nerve fiber action potentials are in fact significantly different from that elicited by simple bath application of exogenous neurotransmitters to isolated arteries (a common experimental technique), and end by identifying important questions remaining in our understanding of sympathetic neurotransmission and the physiological regulation of contraction of small arteries.