Purinergic P2X7 Receptors Mediate ATP-induced Saliva Secretion by the Mouse Submandibular Gland

Tetsuji Nakamoto,David A Brown,Marcelo A Catalán,Mireya Gonzalez-Begne,Victor G Romanenko,James E Melvin

doi:10.1074/jbc.m808597200

Tetsuji Nakamoto, David A Brown + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m808597200

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Abstract

Salivary glands express multiple isoforms of P2X and P2Y nucleotide receptors, but their in vivo physiological roles are unclear. P2 receptor agonists induced salivation in an ex vivo submandibular gland preparation. The nucleotide selectivity sequence of the secretion response was BzATP >> ATP > ADP >> UTP, and removal of external Ca(2+) dramatically suppressed the initial ATP-induced fluid secretion ( approximately 85%). Together, these results suggested that P2X receptors are the major purinergic receptor subfamily involved in the fluid secretion process. Mice with targeted disruption of the P2X(7) gene were used to evaluate the role of the P2X(7) receptor in nucleotide-evoked fluid secretion. P2X(7) receptor protein and BzATP-activated inward cation currents were absent, and importantly, purinergic receptor agonist-stimulated salivation was suppressed by more than 70% in submandibular glands from P2X(7)-null mice. Consistent with these observations, the ATP-induced increases in [Ca(2+)](i) were nearly abolished in P2X(7)(-/-) submandibular acinar and duct cells. ATP appeared to also act through the P2X(7) receptor to inhibit muscarinic-induced fluid secretion. These results demonstrate that the ATP-sensitive P2X(7) receptor regulates fluid secretion in the mouse submandibular gland.

Highlights

Our results revealed that ATP acts in isolation to stimulate fluid secretion from the mouse submandibular gland, but secretion is inhibited when ATP is simultaneously presented with a muscarinic receptor agonist
To test this hypothesis we employed an ex vivo, perfused mouse Submandibular Gland (SMG) organ system. This ex vivo technique allows for precise control of the content of the vascular perfusate and ameliorates the rapid degradation of purinergic receptor agonists observed in vivo
We show that purinergic stimulation results in a sustained, extracellular Ca2ϩ-dependent secretion of saliva in an intact mouse submandibular salivary gland preparation

Summary

Introduction

Given that activation of P2X and P2Y receptors evokes an increase in [Ca2ϩ]i in salivary gland cells, purinergic stimulation of either subfamily might be expected to result in fluid secretion (2). Re-addition of extracellular Ca2ϩ resulted in a modest recovery of the fluid secretion flow rate (Fig. 2B, black versus gray trace at 6 –10-min stimulation).

Results

Conclusion