Diltiazem components

Key findings that demonstrated that the 0 subunit is the essential component of L-type channels have come from studies of the channel activity of the expressed protein. Expression studies performed in mammalian liver fibroblasts have demonstrated that the oti subunit alone can form a channel [77] and contains the receptors for the DHPs, PAAs and diltiazem [64]. In very elegant studies using a mouse model of muscular dysgenesis it has been demonstrated that the ] subunit DNA can restore Ca currents and the charge movement that arises from the voltagesensing function of the channels to the mutant cells that normally lack these activities [21,78,79]. The restoration of these activities restores excitation-contraction coupling. Thus it is clear that the aj subunit is the major functional unit of L-type Ca channels. 

BK currents consisted of transient and steady-state components. The transient currents were abolished by ryanodine (10 fiM), indicating that they are activated by Ca2+ sparks. The lag from the onset of depolarization (activation of VDCCs) to the first transient BK current was around 50 ms. This delay is much too long to be attributed to local signalling from VDCCs to RyRs such as occurs in heart, and instead is consistent with the idea of loose coupling between VDCCs and RyRs (Fig. 1 A) (Collier et al 2000). Spark-activated transient BK currents remained in the presence of the VDCC antagonist diltiazem (50 //M). However, the frequency of... 

SIL CN column (5 pm particle size, 150 mm x 4.6 mm I.D.) and a mobile phase of 0.05M aqueous potassium phosphate (monobasic) solution containing 0.05% (v/v) triethylamine (pH 4.0) acetonitrile (75 25). The separation is achieved at ambient temperature using a flow rate of 1.0 mL/minute. UV absorbance detection is accomplished at a wavelength of 236 nm. The standard and sample solutions are prepared in a diluent of acetonitrile and 20 pL are injected onto the column. The retention time of diltiazem is approximately 13 minutes while that of the potential degradation product, desacetyl diltiazem, is 9 minutes. The analysis is completed within 17 minutes and allows quantitation of both components. A typical HPLC chromatogram is shown in Figure 14. 

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