Transient receptor potential canonical channels are a family of non-selective cation channels (TRPC1-7) that are thought to form pathways for both store- and receptor-operated calcium entry (McFadzean & Gibson, 2002). TRPC3, 6 and 7 are unique amongst cation channels in being directly activated by the signalling molecule, diacylglycerol. We have previously shown that TRPC1 and TRPC6 proteins are expressed in rat mesenteric artery vascular smooth muscle (Hill et al, 2002). The aim of the present study was to investigate the currents elicited by the α₁ adrenoceptor agonist, phenylephrine (PE) and the diacylglycerol analogue, 1-oleoyl-2-acetyl-sn-glycerol (OAG).Male rats were killed according to UK legislation and mesenteric arterial smooth muscle cells isolated using a protocol modified from Hayabuchi et al, 2001. Membrane currents were recorded in the whole-cell patch-clamp configuration from a holding potential of −60mV using a K⁺-rich pipette solution. When required, 10mM tetraethylammonium chloride (TEA) was used to block voltage-gated K⁺ currents. Current-voltage (IV) relations in the absence and presence of drugs were obtained using a ramp protocol (−100 to +40mV). Data are expressed as mean ± SEM. In the presence of internal K⁺,10µM PE induced an outwardly rectifying current that developed positive to −30mV, and reached a peak difference current of 59±20pA (n=7) at +40mV. Similarly, 100µM OAG activated an outwardly rectifying current that developed positive to −30mV, reaching its peak difference current of 43±16pA (n=7) at +40mV. In 3 of 7 cells, the development of this outward current was preceded by inhibition of peak current at +40mV of 37±5%. We investigated the effect that a change in the dominant cation in the intracellular (pipette) solution would have on the response to 100µM OAG, by equimolar replacement of K⁺ with Cs⁺. 100µM OAG still elicited an outwardly rectifying current which developed positive to −15mV and reached a peak difference current of 279±61 pA at +40mV (n=9). No inhibitory effect on peak current was observed prior to current development; however between −15mV and −80mV there was an inward component to the IV trace (reaching a maximum of −78±18pA at −35mV). The responses to 100µM OAG using a Cs⁺ -rich intracellular solution were not inhibited by the protein kinase C inhibitor GF109203X (1µM). We conclude that PE and OAG induce currents displaying similar IV relationships, bearing some resemblance to that of TRPC6.