Stimulation of P2 purinergic receptors increases calcium (Ca) spark frequency in ventricular cardiac myocytes (CMs) from transgenic (TG) mice with cardiac specific overexpression of the human P2X4 receptor

Abstract

Small local increases in cytosolic Ca occur in resting CMs. These are referred to as Ca sparks, and have been determined to be unitary sarcoplasmic reticulum (SR) Ca release events. Studies of CMs from TG mice have shown that SR Ca load, Ca transient amplitude and contractility are increased by purinergic agonists. Our objective was to determine if the elevation in SR Ca load in TG CMs was related to alterations in Ca spark events recorded from TG CMs. CMs acutely isolated from the hearts of TG or wild type (WT) mice were loaded with Fluo‐4 AM. CMs were superfused with a modified Tyrode's solution (22°C), in the presence or absence of the P2 receptor agonist 2MeS‐ATP (3 μM). Ca sparks were recorded with a Zeiss LSM 510. Under basal conditions, Ca spark frequency in TG CMs did not differ from WT (1.49 ± 0.32 vs 0.83 ± 0.31 sparks/100μm/s ± SEM, 2‐way ANOVA, SNK posttest, p = 0.14, n = 24 & 25). The frequency of sparks in the presence of 2MeS‐ATP was significantly greater in TG than in WT CMs (3.10 ± 0.32 vs 1.10 ± 0.31, p < 0.01, n = 24 & 25). In 7 of 25 WT CMs P2 stimulation significantly increased Ca spark frequency, from 1.00 ± 0.28 to 2.81 ± 0.40 (p < 0.01) sparks/100μm/s. Ca spark properties such as amplitude, width, duration and time to peak remained unchanged in all conditions. Thus, the P2 agonist‐induced increase in SR Ca load in TG CMs is related to an increase in Ca spark frequency, but not to altered Ca spark properties. Research support from NIH‐NHLBI.