Purinoceptors in the preglomerular renal resistance arteries regulate arterial diameter via P2X-purinoceptor (P2X-R) -mediated vasoconstriction and P2Y-purinoceptor -mediated vasodilatation [1] and, therefore, play an important role in the regulation of renal blood flow and glomerular filtration rate. Selective P2X-R stimulation increases [Ca²⁺]_i in renal vascular smooth muscle cells (RVSMCs) freshly isolated from the preglomerular microvasculature [2] and triggers contraction of these myocytes. The aim of this work was to study at sub-cellular level the dynamics of [Ca²⁺]_i mobilisation and restoration following stimulation of P2X-R in RVSMCs. Experiments were performed on single RVSMCs freshly isolated from arcuate and interlobular arteries, and afferent arterioles, which were separated from rat kidney using an iron oxide sieving technique [3]. Changes of [Ca²⁺]_i in the cells loaded with the high affinity Ca2+ indicator Fluo-4 AM were visualised using fast (33-40 Hz) x-y confocal imaging. Data are presented as mean ± S.E.M. Gene expression was assessed with RT-PCR technique. At rest freshly isolated RVSMCs revealed spontaneous Ca²⁺ sparks and Ca²⁺ waves. Stimulation of P2X-Rs (ionotropic receptors [2]) with 10 μM α,β-methylene adenosine 5’-triphosphate (AMP-CPP) evoked a fast (mean time-to-peak 0.72±0.06 s; n=13) sub-plasmalemmal [Ca²⁺]_i upstroke (SPCU). This was two times faster than SPCU induced by stimulation of α₁-adrenoceptors (metabotropic receptors [2]). The SPCU was followed by a global rise of [Ca²⁺]_i, which consisted of transient and sustained components [4], with the full duration at half-maximal amplitude of 4.08±0.30 s (n=19). The AMP-CPP-induced [Ca²⁺]_i mobilisation was closely followed (with a delay of 1.02±0.17 s; n=14) by a rise of mitochondrial [Ca²⁺] detected with Rhod-2. The relation of spatial patterns of AMP-CPP-induced [Ca²⁺]_i transients to the intracellular distribution of mitochondria and elements of sarcoplasmic reticulum (SR) suggests that: (1) spatial non-uniformities in SCPU are consistent with Ca²⁺ release from discrete sub-PM SR elements; (2) these SR elements are in close juxtaposition with mitochondria. RT-PCR analysis confirmed expression in single RVSMCs of genes encoding P2X₁-Rs, but not P2X₃-Rs or P2X₅-Rs. Our results demonstrated that activation of P2X₁-purinoceptors in RVSMCs evokes a significantly faster SPCU followed by a significantly shorter global [Ca²⁺]_i rise than in the case of α₁-adrenoceptor activation. It was also shown that these [Ca²⁺]_i transients are associated with mitochondrial Ca²⁺ uptake, thus suggesting a tight functional interaction between mitochondria and SR in RVSMCs. The mechanisms involved in genesis of P2X-R-induced SPCU are under current investigation.