Ca 2؉ influx through L-type Ca 2؉ channels (LTCCs) influences numerous physiological processes ranging from contraction in muscle and memory in neurons to gene expression in many cell types. However, the spatiotemporal organization of functional LTCCs has been nearly impossible to investigate because of methodological limitations. Here, we examined LTCC function with high temporal and spatial resolution using evanescent field fluorescence microscopy. Surprisingly, we found that LTCCs operated in functionally organized clusters, not necessarily as individual proteins. Furthermore, LTCC function in these clusters does not appear to be controlled by simple stochastic gating but instead by a PKCdependent switch mechanism. This work suggests that resting intracellular free calcium concentration in arterial myocytes is predominantly controlled by this process in combination with rare voltage-dependent openings of individual LTCCs. We propose that Ca 2؉ influx via persistent LTCCs may be an important mechanism regulating steady-state local and global Ca 2؉ signals.evenescent field microscopy ͉ smooth muscle ͉ sparklets

Abstract-Hypertension is a perplexing multiorgan disease involving renal primary pathology and enhanced angiotensin II vascular reactivity. Here, we report that a novel form of a local Ca 2ϩ signaling in arterial smooth muscle is linked to the development of angiotensin II-induced hypertension. Key Words: L-type Ca 2ϩ channels Ⅲ protein kinase C Ⅲ myogenic tone Ⅲ total internal reflection fluorescence microscopy H ypertension is a major risk factor for the development of stroke, coronary artery disease, heart failure, and renal disease. 1 Although the principal cause of hypertension is renal, vascular dysfunction is critical, 2 and the increased arterial tone associated with hypertension contributes to the development of the pathology. This is highlighted by recent studies indicating that the endogenous vasoconstrictor angiotensin II is a likely contributor to vascular dysfunction in human 3,4 and model [5][6][7][8][9][10][11][12][13] hypertension. Accordingly, the angiotensin II signaling system is the target for two major classes of pharmacological agents (angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists) that are widely used clinically for the treatment of hypertension in humans. At present, however, the molecular mechanisms by which angiotensin II signaling causes vascular dysfunction and contributes to hypertension are unclear. Here, we address that conundrum and provide a novel and surprising answer.Increased L-type Ca 2ϩ channel activity in arterial myocytes is thought to be necessary for the development of vascular dysfunction during hypertension. 9,11,14 -17

Abstract-Depressed contractility of failing myocytes involves a decreased rate of rise of the Ca 2ϩ transient. Synchronization of Ca 2ϩ release from the junctional sarcoplasmic reticulum (SR) is responsible for the rapid rise of the normal Ca 2ϩ transient. This study examined the idea that spatially and temporally dyssynchronous SR Ca 2ϩ release slows the rise of the cytosolic Ca 2ϩ transient in failing feline myocytes. Left ventricular hypertrophy (LVH) with and without heart failure (HF) was induced in felines by constricting the ascending aorta. Ca 2ϩ transients were measured in ventricular myocytes using confocal line scan imaging. Ca 2ϩ transients were induced by field stimulation, square wave voltage steps, or action potential (AP) voltage clamp. SR Ca 2ϩ release was significantly less well spatially and temporally synchronized in field-stimulated HF versus control or LVH myocytes. Surprisingly, depolarization of HF cells to potentials where Ca 2ϩ currents (I Ca ) were maximal resynchronized SR Ca 2ϩ release. Correspondingly, decreases in the amplitude of I Ca desynchronized SR Ca 2ϩ release in control, LVH, and HF myocytes to the same extent. HF myocytes had significant loss of phase 1 AP repolarization and smaller I Ca density, which should both reduce Ca 2ϩ influx. When normal myocytes were voltage clamped with HF AP profiles SR Ca 2ϩ release was desynchronized. SR Ca 2ϩ release becomes dyssynchronized in failing feline ventricular myocytes because of reductions in Ca 2ϩ influx induced in part by alterations in early repolarization of the AP. Therefore, therapies that restore normal early repolarization should improve the contractility of the failing heart. (Circ Res. 2005;96:543-550.) Key Words: heart failure Ⅲ excitation contraction coupling Ⅲ sarcoplasmic reticulum Ⅲ calcium transients H emodynamic overload induces cardiac hypertrophy and alterations in the contractile properties of the resident cardiac myocytes, both of which can help the heart maintain cardiac output. However, when the hemodynamic stress is persistent, the heart usually makes a transition from compensated hypertrophy to a progressively deteriorating functional state termed congestive heart failure (CHF). This transition is known to be associated with alterations in the magnitude, duration, and kinetics of the systolic Ca 2ϩ transient. Multiple cellular and molecular changes are thought to underlie the abnormal Ca 2ϩ transient of the hypertrophied/ failing myocyte. [1][2][3][4][5][6][7] The reduced size and prolonged duration of the Ca 2ϩ transient involves reduced sarcoplasmic reticulum (SR) Ca 2ϩ stores 1,7-9 resulting from a slowed rate of SR Ca 2ϩ uptake. This reduced SR function is thought to be caused by reductions in the density of the SR Ca 2ϩ ATPase (SERCA) 10 -12 and by reduced phosphorylation of the SERCA inhibitory protein phospholamban (PLB). [13][14][15] There is also some evidence for an increased rate of Ca 2ϩ "leak" from the SR through "hyperphosphorylated" Ca 2ϩ release channels (ryanodine receptors, RYR). 16,17 R...