The effects of phosphocreatine introduced simultaneously into many cardiac cells

Acute creatine loading increases fat-free mass, but does not affect blood pressure, plasma creatinine, or CK activity in men and women

Creatine monohydrate (CrM) administration may enhance high intensity exercise performance and increase body mass, yet few studies have examined for potential adverse effects, and no studies have directly considered potential gender differences.

PURPOSE

The purpose of this study was to examine the effect of acute creatine supplementation upon total and lean mass and to determine potential side effects in both men and women.

METHODS

The effect of acute CrM (20 g x d(-1) x 5 d) administration upon systolic, diastolic, and mean BP, plasma creatinine, plasma CK activity, and body composition was examined in 15 men and 15 women in a randomized, double-blind experiment. Additionally, ischemic isometric handgrip strength was measured before and after CrM or placebo (PL).

RESULTS

CrM did not affect blood pressure, plasma creatinine, estimated creatinine clearance, plasma CK activity, or handgrip strength (P > 0.05). In contrast, CrM significantly increased fat-free mass (FFM) and total body mass (P < 0.05) as compared with PL, with no changes in body fat. The observed mass changes were greater for men versus women.

CONCLUSIONS

These findings suggest that acute CrM administration does not affect blood pressure, renal function, or plasma CK activity, but increases FFM. The effect of CrM upon FFM may be greater in men as compared with that in women.

Phosphotransfer reactions in the regulation of ATP-sensitive K+ channels

ATP-sensitive K+ (K(ATP)) channels are nucleotide-gated channels that couple the metabolic status of a cell with membrane excitability and regulate a number of cellular functions, including hormone secretion and cardioprotection. Although intracellular ATP is the endogenous inhibitor of K(ATP) channels and ADP serves as the channel activator, it is still a matter of debate whether changes in the intracellular concentrations of ATP, ADP, and/or in the ATP/ADP ratio could account for the transition from the ATP-liganded to the ADP-liganded channel state. Here, we overview evidence for the role of cellular phosphotransfer cascades in the regulation of K(ATP) channels. The microenvironment of the K(ATP) channel harbors several phosphotransfer enzymes, including adenylate, creatine, and pyruvate kinases, as well as other glycolytic enzymes that are able to transfer phosphoryls between ATP and ADP in the absence of major changes in cytosolic levels of adenine nucleotides. These phosphotransfer reactions are governed by the metabolic status of a cell, and their phosphotransfer rate closely correlates with K(ATP) channel activity. Adenylate kinase catalysis accelerates the transition from ATP to ADP, leading to K(ATP) channel opening, while phosphotransfers driven by creatine and pyruvate kinases promote ADP to ATP transition and channel closure. Thus, through delivery and removal of adenine nucleotides at the channel site, phosphotransfer reactions could regulate ATP/ADP balance in the immediate vicinity of the channel and thereby the probability of K(ATP) channel opening. In this way, phosphotransfer reactions could provide a transduction mechanism coupling cellular metabolic signals with K(ATP) channel-associated functions.