Different responses of the blockade of the P2Y1 receptor with BPTU in human and porcine intestinal tissues and in cell cultures

Background: Gastrointestinal smooth muscle relaxation is accomplished by activation of P2Y₁ receptors, therefore this receptor plays an important role in regulation of gut motility. Recently, BPTU was developed as a negative allosteric modulator of the P2Y₁ receptor. Accordingly, the aim of this study was to assess the effect of BPTU on purinergic neurotransmission in pig and human gastrointestinal tissues. Methods: Ca²⁺ imaging in tSA201 cells that express the human P2Y₁ receptor, organ bath and microelectrodes in tissues were used to evaluate the effects of BPTU on purinergic responses. Key results: BPTU concentration dependently (0.1 and 1 µmol L⁻¹) inhibited the rise in intracellular Ca²⁺ evoked by ADP in tSA201 cells. In the pig small intestine, 30 µmol L⁻¹ BPTU reduced the fast inhibitory junction potential by 80%. Smooth muscle relaxations induced by electrical field stimulation were reduced both in pig ileum (EC₅₀ = 6 µmol L⁻¹) and colon (EC₅₀ = 35 µmol L⁻¹), but high concentrations of BPTU (up to 100 µmol L⁻¹) had no effect on human colonic muscle. MRS2500 (1 µmol L⁻¹) abolished all responses. Finally, 10 µmol L⁻¹ ADPβS inhibited spontaneous motility and this was partially reversed by 30 µmol L⁻¹ BPTU in pig, but not human colonic tissue and abolished by MRS2500 (1 µmol L⁻¹). Conclusions & inferences: BPTU blocks purinergic responses elicited via P2Y₁ receptors in cell cultures and in pig gastrointestinal tissue. However, the concentrations needed are higher in pig tissue compared to cell cultures and BPTU was ineffective in human colonic tissue.