Glaucoma, capillaries and pericytes .5. Preliminary evidence that carbon dioxide relaxes pericyte contractile tone

We undertook this study to determine if pericytes respond to carbon dioxide in a manner such that they could help control capillary blood flow and that their physiologic responses to pCO(2) might be worthy of detailed study. Pericytes were isolated from bovine retinas and grown in cell culture. Changes in the contractile tone of the pericytes upon changing the ambient pCO(2) were observed by noting changes in the wrinkling of an elastic silicone surface on which they were grown. An increase in pCO(2) caused acidosis of the medium and relaxation of the pericytes in a reversible, concentration-dependent manner. These findings suggest that the regulation of blood flow to meet local metabolic needs does not reside entirely in the arterioles and precapillary sphincters, but at least in part in the capillary bed through the contractile properties of pericytes. The focal pCO(2) is one of several potential indicators of whether or not local blood flow is adequate for local tissue needs. The response to local conditions may modulate or be modulated by the effect of neurotransmitters and hormones on the local rate of blood flow.