Dopamine activates ATP-sensitive K+ currents in rat retinal pericytes

The relatively sparse vasculature of the retina minimizes obstruction to incoming light, but also poses a challenge to fulfilling the metabolic demands of retinal neurons. An efficient process for distributing energy supplies to areas of need is likely to involve neuron-derived vasoactive signals. However, knowledge of the mechanisms by which capillary perfusion is regulated by neuron-to-vascular signaling is limited. Potential targets of vasoactive molecules released from nerve cells are the pericytes, which are positioned on the endothelial walls of microvessels and are thought to play a role in controlling the microcirculation. In this study, we assessed the effect of dopamine on pericyte physiology. Because dopaminergic neurites are closely associated with microvessels that express dopamine receptors, this molecule is a putative neuron-to-capillary signal, as well as neurotransmitter. We used the perforated-patch configuration of the patch-clamp technique to monitor the whole-cell currents of pericytes located on microvessels freshly isolated from the adult rat retina. In 43% (58/134) of the sampled pericytes, we found that dopamine reversibly activated a hyperpolarizing current, which increased the membrane potential by 19 +/- 1 mV. This dopamine-induced current was inhibited by the ATP-sensitive potassium (KATP) channel blocker, glibenclamide. Consistent with a signaling pathway involving D1 dopamine receptors, adenylate cyclase and protein kinase A (PKA), the selective D1 antagonist, SCH23390, inhibited the hyperpolarizing effect of dopamine; the activator of adenylate cyclase, forskolin, mimicked the dopaminergic effect, and H89, which inhibits PKA, significantly reduced the hyperpolarization induced by dopamine. Taken together, our experiments indicate that a mechanism involving D1 dopamine receptors, adenylate cyclase, and PKA activates KATP currents in retinal pericytes. Our observations support the hypothesis that, in addition to being a neuromodulator, dopamine also serves as a signal linking neuronal activity with the function of the pericyte-containing microvasculature.