Investigation of the relationship between stimulus parameters and a human muscle contraction force during stimulation of the gastrocnemius muscle.

The article presents the results of investigations on the influence of biphasic stimulus parameters such as duration and stimulus interphase interval (IPI) on a gastrocnemius muscle contraction force. Seven healthy volunteers participated in this experiment, and 24 different stimuli patterns were tested. Special attention was paid to the comfort level of a sensory perception while the electrostimulation was applied. During the test, an optimal stimulus pattern evoking contraction at the level over 15% maximum voluntary contraction force and preserving a good comfort perception reported by all of the participants was investigated. It was found that bursts of pulses with width 175 micros and the IPI from 50 to 1000 micros satisfied these criteria. Moreover, it was observed that the increase of the IPI duration generated a significantly stronger contraction force in comparison with the stimulation with the standard biphasic pulses (IPI = 0 micros) having the same amplitude, frequency, and pulse duration. This shows that the modulation of the IPI might be a potentially useful support for the standard force-control methods and may find an application in neuromuscular electrical stimulation systems.

An alternative splice variant in Abcc6, the gene causing dystrophic calcification, leads to protein deficiency in C3H/He mice.

Dystrophic cardiac calcification (DCC) is an autosomal recessive trait characterized by calcium phosphate deposits in myocardial tissue. The Abcc6 gene locus was recently found to mediate DCC; however, at the molecular level the causative variants remain to be determined. Examining the sequences of Abcc6 cDNA in DCC-resistant C57BL/6 and DCC-susceptible C3H/He mice, we identified a missense mutation (Cys to Thr at codon 619, rs32756904) at the 3'-border of exon 14 that creates an additional donor splice site (GT). Accordingly, an alternative transcript variant was detected, lacking the last 5 bp of exon 14 (-AGG(C/T)GCTgtga-) in DCC-susceptible C3H/He mice that carry the Thr allele. The 5-bp deletion was found to result in premature termination at codon 684, in turn leading to protein deficiency in DCC-susceptible mouse tissue as well as in cells transfected with Abcc6 cDNA lacking the last 5 bp of exon 14. All mouse strains that were found to carry the Thr allele, including C3H/He, DBA/2J, and 129S1/SvJ, were also found to be positive for DCC. In summary, we identified a splice variant leading to a 5-bp deletion in the Abcc6 transcript that gives rise to protein deficiency both in vivo and in vitro. The fact that all mouse strains that carry the deletion also develop dystrophic calcifications further suggests that the underlying splice variant affects the biological function of MRP6 protein and is a cause of DCC in mice.