Structural requirements of steroidal agonists of transient receptor potential melastatin 3 (TRPM3) cation channels.

BACKGROUND AND PURPOSE: Transient receptor potential melastatin 3 (TRPM3) proteins form non-selective but calcium-permeable membrane channels, rapidly activated by extracellular application of the steroid pregnenolone sulphate and the dihydropyridine nifedipine. Our aim was to characterize the steroid binding site by analysing the structural chemical requirements for TRPM3 activation. EXPERIMENTAL APPROACH: Whole-cell patch-clamp recordings and measurements of intracellular calcium concentrations were performed on HEK293 cells transfected with TRPM3 (or untransfected controls) during superfusion with pharmacological substances. KEY RESULTS: Pregnenolone sulphate and nifedipine activated TRPM3 channels supra-additively over a wide concentration range. Other dihydropyridines inhibited TRPM3 channels. The natural enantiomer of pregnenolone sulphate was more efficient in activating TRPM3 channels than its synthetic mirror image. However, both enantiomers exerted very similar inhibitory effects on proton-activated outwardly rectifying anion channels. Epiallopregnanolone sulphate activated TRPM3 almost equally as well as pregnenolone sulphate. Exchanging the sulphate for other chemical moieties showed that a negative charge at this position is required for activating TRPM3 channels. CONCLUSIONS AND IMPLICATIONS: Our data demonstrate that nifedipine and pregnenolone sulphate act at different binding sites when activating TRPM3. The latter activates TRPM3 by binding to a chiral and thus proteinaceous binding site, as inferred from the differential effects of the enantiomers. The double bond between position C5 and C6 of pregnenolone sulphate is not strictly necessary for the activation of TRPM3 channels, but a negative charge at position C3 of the steroid is highly important. These results provide a solid basis for understanding mechanistically the rapid chemical activation of TRPM3 channels.

A compartmental model for alveolar clearance of pertechnegas.

UNLABELLED: The washout of an inhaled water soluble radiotracer from the lungs is a measure of alveolar integrity. Data evaluation of 99mTc-DTPA studies were previously performed mainly with monoexponential fitting with or without background subtraction. The introduction of 99mTc-pertechnegas for the assessment of alveolar permeability necessitates the investigation of adequate data evaluation schemes for this radiotracer. METHODS: We developed a three-compartmental model to describe 99mTc-pertechnegas kinetics after inhalation. Monoexponential fitting of the first 5 min was investigated as simplification for clinical use. Different background corrections based on blood samples or representative regions of interest were compared. RESULTS: Correction of intra- and extravascular background by subtraction of calibrated curves, which are derived from blood or background areas, resulted in monoexponential washout curves. Clearance rates based on the three-compartmental model were nearly the same as those derived from a monoexponential fit after blood-activity subtraction (r = 0.96). A monoexponential analysis of the first 5 min without any background correction correlates well with the first component of the biexponential analysis (r = 0.97). CONCLUSION: A dynamic study of more than 45 min allows quantitative determination of the transfer rate of 99mTc-pertechnegas from the alveoli into the blood using compartmental analysis. A simplified monoexponential analysis of the first 5 min allows assessment of lung clearance without any background correction.

Biomechanical alterations in the carpal arch and hand muscles after carpal tunnel release: a further approach toward understanding the function of the flexor retinaculum and the cause of postoperative grip weakness.

The difference between maximal and minimal distance covered (the distance between the trapezium ridge and hamate hook; moment exerted on structures: 1 Nm) by an intact flexor retinaculum (FR; minimum, 3.3 +/- 0.1 cm; maximum, 3.7 +/- 0.2 cm) and the increase in the maximal distance on carpal tunnel release (CTR; increase, 1.6 +/- 0.2 mm) were significant. Under an external supination moment, the distance between the attachments of the trapeziopisiform band increased after CTR. Under external pronation and ulnar abduction moments, the distance between the attachments of the scaphoideohamate band increased after CTR. The CTR resulted in an anatomic attachment loss for the following muscles: the superficial head of the flexor pollicis brevis (shortening by approximately 25%, relative to rest length), the ulnar part of the abductor pollicis brevis (with opposition and adductory functions, approximately 20%), the opponens pollicis (approximately 20%), the middle part of the abductor pollicis brevis (approximately 7%), and the opponens digiti minimi (approximately 10%). Preoperative and postoperative (2-7 weeks after surgery) measurements of the reaction force of the distal phalanx (under isometric thumb opposition and finger II-IV flexion with extended carpal joint) led to differentiation of three groups: (1) significant strength loss--the patients showed difficulties with grasping, lifting, twisting off lids and caps, screwing, pulling ropes, and pinching; (2) no significant change in force values; and (3) a significant increase in strength (patients who could grip more firmly).