Different purinergic receptors lead to intracellular calcium increases in pancreatic ducts

Abstract

Extracellular adenosine 5'-triphosphate (ATP) has been described to act as a regulator in many cells and tissues, including epithelia, and in the gastrointestinal tract ATP is one of the substances involved in non-cholinergic non-adrenergic control. However, very little is known about the effect of ATP on pancreatic ducts, which normally secrete bicarbonate-rich fluid in response to secretin. Hence, the aim of our present study was to test the effect of ATP and other nucleotides on intracellular Ca2+ activity ([Ca2+]i) of pancreatic ducts, and thereby get information about purinergic receptors that might play a role in the regulation of pancreatic bicarbonate transport. Native intralobular ducts were obtained from rat pancreas and [Ca2+]i in 10-20 cells was measured using the fura-2 method. ATP (10(-4) mol/l) evoked a characteristic biphasic Ca2+ transient in duct cells. Nucleotides, used to classify the P2 receptors, acted with the following potency on the peak Ca2+ in many ducts: uridine 5'-triphosphate (UTP) >/= ATP >inosine 5'-triphosphate >/= 2-methylthio-ATP > beta,gamma-methyl-ATP > adenosine. However, although the peak [Ca2+]i responses to ATP and UTP were similar, the plateau [Ca2+]i was nearly doubled with UTP. Moreover, in about one-third of the ducts studied, UTP had no effect on cell Ca2+, while the response to ATP was normal. In further experiments we found that removal of extracellular Mg2+ increased the peak [Ca2+]i evoked in response to ATP. 2'&3'-O-(4-benzoylbenzoyl) ATP (BzATP) evoked a monophasic and slower increase in [Ca2+]i, which was inhibited by removal of extracellular Ca2+, or by addition of 4,4'-diisothiocyanatostilbene-2, 2'-disulphonic acid (DIDS). Taken together, our data indicate that there are two types of purinergic receptors on pancreatic ducts through which ATP can act. These are pharmacologically known as P2U and P2Z receptors and may correspond to P2Y2 and P2X7 receptors.

Purinoceptors Evoke Different Electrophysiological Responses in Pancreatic Ducts

“…ATP stimulation, similar to that of acetylcholine, evokes a characteristic biphasic Ca 2ϩ response consisting of a Ca 2ϩ peak and a Ca 2ϩ plateau. The peak response is largely due to release of Ca 2ϩ from intracellular stores, whereas the plateau reflects largely influx of Ca 2ϩ from extracellular medium (36,38). UTP evoked a similar response, but a more pronounced Ca 2ϩ influx component.…”

“…On the other hand, stimulation with BzATP led to a monophasic Ca 2ϩ response, which was almost fully dependent on extracellular Ca 2ϩ and thus due to Ca 2ϩ influx. On the basis of these and other observations, we postulated that there are at least two types of receptors belonging to both P2Y and P2X families (36). Fig.…”

“…Furthermore, we demonstrated that ATP inhibits secretin-evoked changes in the membrane voltage (37). We used Ca 2ϩ signals and pharmacological profiles to describe two types of receptors: one responding to UTP and ATP and belonging to the P2Y superfamily (P2Y 2 -like receptor) and another responding to BzATP 1 and ATP and belonging to the P2X superfamily (P2X 7 -like receptor) (36). Although epithelial P2 receptors are associated with Ca 2ϩ signaling in ducts, it is not clear how this is further translated into ion transport and thus secretion in native pancreatic ducts.…”

Purinergic receptors in the endocrine and exocrine pancreas

“…Detailed analyses of molecular identity and function of P2 receptors were carried out on the rat (and guinea pig) pancreas and therefore this will be the starting and reference point for other numerous studies on human duct lines. In single pancreatic ducts microdissected from the rat pancreas, ATP had a concentration-dependent effect on the membrane potential and it stimulated both Ca 2+ release and Ca 2+ influx with the following potency UTP≥ATP>2-methylthio-ATP>α,β-methylene-ATP≫adenosine [91][92][93][94]. BzATP, which is an agonist for P2X 7 and also other P2X receptors [95], induced fully reversible Ca 2+ and Na + influx.…”

Procedures to characterize and study P2Z/P2X7 purinoceptor: flow cytometry as a promising practical, reliable tool

“…rat pancreatic ducts, Leydig cells, supraoptic neurones and schwann cells (Parker & Snow 1972, Foresta et al 1996, Zoeteweij et al 1996, Christoffersen et al 1998, Grafe et al 1999, Shibuya et al 1999. In these cells the characterized P2 receptor shared some, almost all, or even all P 2Z /P2X 7 pharmacological properties, but it was not able to induce the formation of the large non-specific pore.…”