Relationship between bicarbonate and cyclic nucleotide in the promoting effects on head-to-head agglutination in boar spermatozoa.
OBJECTIVE
To clarify the relationship between bicarbonate and cAMP in the promoting effects on the sperm agglutination.


METHODS
Spermatozoa were collected from mature boars, washed and resuspended in a modified Krebs-Ringer HEPES lacking calcium chloride (mKRH). The sperm suspensions were incubated in a water bath (38.5 degrees C) for 60 min and then the percentage of head-to-head agglutinated spermatozoa was determined.


RESULTS
Supplementation of the mKRH with sodium bicarbonate (5-10 mM) significantly raised the percentage of head-to-head agglutinated spermatozoa in the samples. The addition of selective inhibitors for calcium/calmodulin-dependent phosphodiesterases (type 1: 8-methoxymethyl-IBMX and vinpocetine, 25-50 micro M) or for cAMP-specific phosphodiesterases (type 4: Ro20-1724 and rolipram, 25-50 microM) enhanced the effect of bicarbonate on sperm agglutination as highly as did the addition of non-selective inhibitors for phosphodiesterases (IBMX and papaverine, 25-50 microM). A calmodulin antagonist (W-7, 2 microM), that potentially blocks the stimulator of the calcium/calmodulin-dependent phosphodiesterases, significantly enhanced the effect of bicarbonate on sperm agglutination. Moreover, a phosphodiesterase-resistant cAMP analogue (cBiMPS, 0.1 mM) markedly induced agglutination in more spermatozoa (76%) after the incubation without bicarbonate and phosphodiesterase inhibitors than did a less potent cAMP analogue (dibutyryl cAMP, 1 mM) (21%), while three kinds of cGMP analogues (0.1-1 mM) had no effect on sperm agglutination. In addition, a cAMP antagonist (Rp-cAMPS, 1 mM) significantly reduced the sperm agglutination resulting from the actions of bicarbonate and IBMX. On the other hand, the effect of bicarbonate was abolished by a change of incubation temperature from 38.5 degrees C to 25 degrees C.


CONCLUSIONS
These findings demonstrate that the bicarbonate-induced agglutination of boar spermatozoa is controlled via the cAMP-mediated, temperature-dependent signaling cascade. This cascade is suppressed by the action of the phosphodiesterase (at least types 1 and 4).
Harayama
Hiroshi
H
Department of Life Science, Graduate School of Science and Technology, Kobe University, Kobe 657-8501, JAPAN. harayama@ans.kobe-u.ac.jp
Kato
Seishiro
S
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology*; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D006152:Cyclic GMP / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000502:physiology*; D008297:Male; D010208:Papaverine / Q000494:pharmacology; D058915:Purinergic P1 Receptor Antagonists; D017693:Sodium Bicarbonate / Q000494:pharmacology*; D013073:Sperm Agglutination / Q000187:drug effects / Q000502:physiology*; D013077:Sperm Head / Q000187:drug effects / Q000502:physiology*; D013552:Swine; D013806:Theophylline / Q000031:analogs & derivatives* / Q000494:pharmacology
D058915:Purinergic P1 Receptor Antagonists; C016276:8-bromocyclic GMP; C053907:8-cyclopentyl-1,3-dimethylxanthine; D003994:Bucladesine; D017693:Sodium Bicarbonate; D013806:Theophylline; D010208:Papaverine; D000242:Cyclic AMP; D006152:Cyclic GMP; D015056:1-Methyl-3-isobutylxanthine