ADP-mediated Modulation of Intracellular Calcium Responses in Chromaffin Cells: The Role of Ectonucleoside Triphosphate Diphosphohydrolase 2 on Rat Adrenal Medulla Function.

The present study investigated the localization and the adenosine 5'-triphosphate (ATP)-degrading function of the plasma membrane-bound ecto-nucleotidase, ectonucleoside triphosphate diphosphohydrolase 2 (NTPDase2), in the rat adrenal medulla. The effect of ATP degradation product, adenosine 5'-diphosphate (ADP), on carbachol (CCh)-induced intracellular Ca2+ ([Ca2+]i) responses in adrenal chromaffin cells was examined using calcium imaging. NTPDase2-immunoreactive cells were distributed between chromaffin cells. NTPDase2-immunoreactive cells were immunoreactive for glial fibrillary acidic protein and S100B, suggesting that they were sustentacular cells. NTPDase2-immunoreactive cells surrounded chromaffin cells immunoreactive for vesicular nucleotide transporter and P2Y12 ADP-selective purinoceptors. In ATP bioluminescence assays using adrenal medullary slices, ATP was rapidly degraded and its degradation was attenuated by the NTPDase inhibitors sodium polyoxotungstate (POM-1) and 6-N, N-diethyl-d-ß,γ-dibromomethylene ATP (ARL67156). ADP inhibited CCh-induced [Ca2+]i increases of chromaffin cells in adrenal medullary slices. The inhibition of CCh-induced [Ca2+]i increases by ADP was blocked by the P2Y12 purinoceptor antagonist AZD1283. CCh-induced [Ca2+]i increases were also inhibited by the P2Y1, P2Y12, and P2Y13 purinoceptor agonist 2-methylthioadenosine diphosphate trisodium (2MeSADP), in combination with the P2Y1 purinoceptor antagonist MRS2179. These results suggest that sustentacular cells express NTPDase2 to degrade ATP released from adrenal chromaffin cells, and ADP modulates the excitability of chromaffin cells via P2Y12 purinoceptors to regulate catecholamine release during preganglionic sympathetic stimuli. (J Histochem Cytochem 72: 41-60, 2024).

3-Iodothyronamine, a trace amine-associated receptor agonist, regulates intracellular Ca2+ increases via CaMK II through Epac2 in rat cerebral arterioles.

Trace amines (TAs) in the nervous system bind to TA-associated receptors (TAARs) and are involved in the regulation of monoaminergic functions. Among TAAR subtypes, TAAR1 has been implicated in the development of neurological disorders, such as schizophrenia. The present study investigated the effects of the TAAR1 agonist, 3-iodothyronamine (T1AM) on cerebral arterioles using fluctuations in the intracellular concentration of Ca2+ ([Ca2+]i) as an index of contractile responses. In cerebral arterioles, most of the TAAR agonists did not increase [Ca2+]i, while only T1AM elevated [Ca2+]i in vascular smooth muscle cells. This increase involved extracellular Ca2+ influx through T-type Ca2+ channels and inositol trisphosphate- and ryanodine-receptor-mediated Ca2+ release from intracellular stores. The inhibition of the cAMP sensor, exchange protein directly activated by cAMP (Epac) 2, and calmodulin kinase (CaMK) II strongly inhibited Ca2+ elevations. The present study revealed that T1AM acted not only on the TAAR1 receptor as previously suggested, but also on other G-protein coupled receptors and/or signal transduction systems to increase intracellular Ca2+ in cerebral arteriole smooth muscle cells. These results suggest that when using T1AM in clinical practice, attention should be paid to the early rise in blood pressure.