Simultaneous activation of p38 MAPK and p42/44 MAPK by ATP stimulates the K+ current ITREK in cardiomyocytes

Living cells exhibit multiple K(+) channel proteins; among these is the recently reported atypical two-pore domain K(+) channel protein TREK-1. Most K(+) currents are modulated by neurohormones and under various pathological conditions. Here, in rat ventricular cardiomyocytes using the whole-cell patch-clamp technique, we characterize for the first time a native TREK-1-like current (I(TREK)) that is activated by ATP, a purine agonist applied at a micromolar range. This current is sensitive to arachidonic acid, intracellular acidosis, and various K(+) current inhibitors. Reverse transcription-polymerase chain reaction reveals the presence of a TREK-1-like mRNA in rat cardiomyocytes that shows 93% identity with mouse TREK-1. ATP effects are greatly attenuated in the presence of arachidonic acid or HCO(-)(3)-induced intracellular acidosis. Using a series of inhibitors, we further demonstrate that the ATP-induced stimulation of I(TREK) implies the activation of cytosolic phospholipase A(2) and the release of arachidonic acid. These events require the simultaneous involvement of p38 MAPK and p42/44 MAPK, respectively, via a cAMP-dependent protein kinase and a tyrosine kinase pathway, whereas the two MAPKs conjugate to activate a mitogen- and stress-activated protein kinase (MSK-1). Our results thus demonstrate the occurrence of a TREK-1-like current in cardiac cells whose activation by purine agonists implies a dual-MAPK cytosolic pathway.

Ionic basis of ventricular arrhythmias in remodeled rat heart during long-term myocardial infarction

OBJECTIVE

Deleterious electrical abnormalities evolve during myocardial infarction. The goal of this study was to analyse current changes during the late decompensated phase of heart disease induced by coronary ligation and to compare them in various heart regions.

METHODS

Young rats were submitted to left coronary ligature. After 4-6 months, cells were enzymatically dissociated and isolated from the upper part basal region of the left ventricle, as well as from the septum, apex and the right ventricle before being studied under whole-cell patch-clamp.

RESULTS

Basal L-type Ca2+ current, ICaL elicited at +10 mV did not exhibit regional dependence neither in control nor after post-myocardial infarction (PMI). ICaL showed both a significantly reduced peak amplitude (17.1 +/- 2.8 pA/pF versus 9.9 +/- 1.4 pA/pF in seven control and seven PMI hearts, n = 32 and 40, respectively) and a slower inactivation, such that the amount of inward charges during a 200 ms-depolarizing pulse was nearly unchanged. beta-Adrenergic stimulation was less effective in increasing ICaL in PMI cells but it slowed inactivation further. Significant differences in the K+ currents were observed. A regional distribution was seen for Ito only, with the largest amplitude in the right ventricle (in pA/pF: 23.1 +/- 2.4, 18.2 +/- 3.9, 14.8 +/- 2.4, 8.3 +/- 1.7 in the right ventricle, apex, septum and left ventricle, respectively n = 8, 7, 8 and 9). This was also true in failing heart cells despite Ito being halved in each of the four regions (in pA/pF: 12.2 +/- 2.5, 11.2 +/- 1.9, 5.1 +/- 1.0 and 4.8 +/- 1.0, respectively n = 12, 12, 11 and 13). IK1 was also significantly reduced by 20% in the PMI cells. Two-way analyses of variance demonstrated the absence of interaction between the topographical origin of the cells and the physiological state of the rats. The alpha 1-adrenergic agonist, methoxamine significantly reduced Ito and IK1 to the same extent in both sham and PMI cells, by about 35% and 20% respectively.

CONCLUSIONS

Long-term left coronary occlusion induces significant alterations in both Ca2+ and K+ currents that occur with similar amplitude in both ventricles. They include a marked reduction in Ito amplitude as well as a slowing of ICaL inactivation. Both factors could contribute to the disturbances in cellular electrical behaviour and the occurrence of arrhythmias in the post-myocardial infarcted heart.

[Aortic-ventricular tunnel with right coronary artery atresia]

An aortico-left ventricular tunnel was diagnosed at echocardiography in a 6 week old baby after fortuitous detection of a systolic and diastolic murmur. Its association with atresia of the right coronary ostium, suspected at echocardiogoraphy, was confirmed at surgery which included occlusion of the tunnel orifices, aortic commissurotomy and reimplantation of the right coronary artery. The short-term postoperative result is excellent. This is an exceptional malformation, the clinical diagnosis of which is relatively easy. Its relationship with the right coronary artery conforms to an embryological logic and must be investigated thoroughly before surgery to avoid compromising myocardial revascularisation.