Aims/hypothesis  

In a previous study, we demonstrated that a creatine kinase (CK) modulates K_ATP channel activity in pancreatic beta cells. To explore phosphotransfer signalling pathways in more detail, we examined whether K_ATP channel regulation in beta cells is determined by a metabolic interaction between adenylate kinase (AK) and CK.

Methods  

Single channel activity was measured with the patch–clamp technique in the inside-out (i/o) and open-cell attached (oca) configuration.

Results  

The ATP sensitivity of K_ATP channels was higher in i/o patches than in permeabilised beta cells (oca). One reason for this observation could be that the local ATP:ADP ratio in the proximity of the channels is determined by factors not active in i/o patches. AMP (0.1 mmol/l) clearly increased open channel probability in the presence of ATP (0.125 mmol/l) in permeabilised cells but not in excised patches. This suggests that AK-catalysed ADP production in the vicinity of the channels is involved in K_ATP channel regulation. The observation that the stimulatory effect of AMP on K_ATP channels was prevented by the AK inhibitor P ¹,P ⁵-di(adenosine-5′)pentaphosphate (Ap₅A; 20 μmol/l) and abolished in the presence of the non-metabolisable ATP analogue adenosine 5′-(β,γ-imido)triphosphate tetralithium salt (AMP-PNP; 0.12 mmol/l) strengthens this idea. In beta cells from AK1 knockout mice, the effect of AMP was less pronounced, though not completely suppressed. The increase in K_ATP channel activity induced by AMP in the presence of ATP was outweighed by phosphocreatine (1 mmol/l). We suggest that this is due to an elevation of the ATP concentration by CK.

Conclusions/interpretation  

We propose that phosphotransfer events mediated by AK and CK play an important role in determining the effective concentrations of ATP and ADP in the microenvironment of pancreatic beta cell K_ATP channels. Thus, these enzymes determine the open probability of K_ATP channels and eventually the actual rate of insulin secretion.